updated version

EnTT v2

CMakeLists.txt

@@ -16,7 +16,7 @@ endif()
 # Project configuration
 #
 
-project(entt VERSION 1.0.0)
+project(entt VERSION 2.0.1)
 
 if(NOT CMAKE_BUILD_TYPE)
     set(CMAKE_BUILD_TYPE Debug)
@@ -33,15 +33,26 @@ message("* Copyright (c) 2017 ${PROJECT_AUTHOR} <${PROJECT_AUTHOR_EMAIL}>")
 message("*")
 
 #
-# Compile stuff
+# Compiler stuff
 #
 
 set(CMAKE_CXX_STANDARD 14)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
-set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -Wl,--no-undefined")
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pedantic -Wall -Wconversion")
-set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -O0 -g -DDEBUG")
-set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -O3 -DRELEASE")
+
+if(NOT MSVC)
+    set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -Wl,--no-undefined")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pedantic -Wall")
+    set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -DRELEASE")
+    set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -O0 -g -DDEBUG")
+
+    if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+        # it seems that -O3 ruins the performance when using clang ...
+        set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -O2")
+    else()
+        # ... on the other side, GCC is incredibly comfortable with it.
+        set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -O3")
+    endif()
+endif()
 
 #
 # CMake configuration
@@ -54,15 +65,11 @@ set(PROJECT_SRC_DIR ${entt_SOURCE_DIR}/src)
 set(PROJECT_RUNTIME_OUTPUT_DIRECTORY bin)
 
 #
-# Enable test support using ctest-like interface
+# Tests
 #
 
 option(BUILD_TESTING "Enable testing with ctest." ON)
 
-#
-# build testing stuff if required
-#
-
 if(BUILD_TESTING)
     set(THREADS_PREFER_PTHREAD_FLAG ON)
     find_package(Threads REQUIRED)
@@ -78,3 +85,13 @@ if(BUILD_TESTING)
     enable_testing()
     add_subdirectory(test)
 endif()
+
+#
+# Documentation
+#
+
+find_package(Doxygen 1.8)
+
+if(DOXYGEN_FOUND)
+    add_subdirectory(docs)
+endif()

README.md

@@ -1,22 +1,29 @@
-# EnTT - Entity-Component System in modern C++
+# The EnTT Framework
 
-[![Build Status](https://travis-ci.org/skypjack/entt.svg?branch=master)](https://travis-ci.org/skypjack/uvw)
+[![Build Status](https://travis-ci.org/skypjack/entt.svg?branch=master)](https://travis-ci.org/skypjack/entt)
 [![Build status](https://ci.appveyor.com/api/projects/status/rvhaabjmghg715ck?svg=true)](https://ci.appveyor.com/project/skypjack/entt)
 [![Coverage Status](https://coveralls.io/repos/github/skypjack/entt/badge.svg?branch=master)](https://coveralls.io/github/skypjack/entt?branch=master)
+[![Donate](https://img.shields.io/badge/Donate-PayPal-green.svg)](https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=W2HF9FESD5LJY&lc=IT&item_name=Michele%20Caini&currency_code=EUR&bn=PP%2dDonationsBF%3abtn_donateCC_LG%2egif%3aNonHosted)
 
 # Introduction
 
-`EnTT` is a header-only, tiny and easy to use Entity-Component System in modern C++.<br/>
-ECS is an architectural pattern used mostly in game development. For further details:
+`EnTT` is a header-only, tiny and easy to use framework written in modern
+C++.<br/>
+It's entirely designed around an architectural pattern pattern called _ECS_ that
+is used mostly in game development. For further details:
 
 * [Entity Systems Wiki](http://entity-systems.wikidot.com/)
 * [Evolve Your Hierarchy](http://cowboyprogramming.com/2007/01/05/evolve-your-heirachy/)
 * [ECS on Wikipedia](https://en.wikipedia.org/wiki/Entity%E2%80%93component%E2%80%93system)
 
+Originally, `EnTT` was written as a faster alternative to other well known and
+open source entity-component systems.<br/>
+After a while the codebase has grown and more features have become part of the
+framework.
+
 ## Code Example
 
 ```cpp
-#include <iostream>
 #include <registry.hpp>
 
 struct Position {
@@ -29,321 +36,633 @@ struct Velocity {
     float dy;
 };
 
-using ECS = entt::DefaultRegistry<Position, Velocity>;
+void update(entt::DefaultRegistry &registry) {
+    auto view = registry.view<Position, Velocity>();
+
+    for(auto entity: view) {
+        auto &position = view.get<Position>(entity);
+        auto &velocity = view.get<Velocity>(entity);
+        // ...
+    }
+}
 
 int main() {
-    ECS ecs;
+    entt::DefaultRegistry registry;
 
     for(auto i = 0; i < 10; ++i) {
-        auto entity = ecs.create();
-        ecs.assign<Position>(entity, i * 1.f, i * 1.f);
-        if(i % 2 == 0) { ecs.assign<Velocity>(entity, i * .1f, i * .1f); }
+        auto entity = registry.create();
+        registry.assign<Position>(entity, i * 1.f, i * 1.f);
+        if(i % 2 == 0) { registry.assign<Velocity>(entity, i * .1f, i * .1f); }
     }
 
-    std::cout << "single component view" << std::endl;
-
-    for(auto entity: ecs.view<Position>()) {
-        auto &position = ecs.get<Position>(entity);
-        std::cout << position.x << "," << position.y << std::endl;
-    }
-
-    std::cout << "multi component view" << std::endl;
-
-    for(auto entity: ecs.view<Position, Velocity>()) {
-        auto &position = ecs.get<Position>(entity);
-        auto &velocity = ecs.get<Velocity>(entity);
-        std::cout << position.x << "," << position.y << " - " << velocity.dx << "," << velocity.dy << std::endl;
-        if(entity % 4) { ecs.remove<Velocity>(entity); }
-        else { ecs.destroy(entity); }
-    }
-
-    std::cout << "single component view" << std::endl;
-
-    for(auto entity: ecs.view<Position>()) {
-        auto &position = ecs.get<Position>(entity);
-        std::cout << position.x << "," << position.y << std::endl;
-    }
-
-    std::cout << "multi component view" << std::endl;
-
-    for(auto entity: ecs.view<Position, Velocity>()) {
-        auto &position = ecs.get<Position>(entity);
-        auto &velocity = ecs.get<Velocity>(entity);
-        std::cout << position.x << "," << position.y << " - " << velocity.dx << "," << velocity.dy << std::endl;
-        if(entity % 4) { ecs.remove<Velocity>(entity); }
-        else { ecs.destroy(entity); }
-    }
-
-    ecs.reset();
+    update(registry);
+    // ...
 }
 ```
 
 ## Motivation
 
-I started using another well known Entity-Component System named [`EntityX`](https://github.com/alecthomas/entityx).<br/>
-While I was playing with it, I found that I didn't like that much the way it manages its memory.
-Moreover, I was pretty sure that one could achieve better performance with a slightly modified pool under the hood.<br/>
-That's also the reason for which the interface is quite similar to the one of `EntityX`, so that `EnTT` can be used as a
-drop-in replacement for it with a minimal effort.
+I started working on `EnTT` because of the wrong reason: my goal was to design
+an entity-component system that beated another well known open source solution
+in terms of performance.<br/>
+I did it, of course, but it wasn't much satisfying. Actually it wasn't
+satisfying at all. The fastest and nothing more, fairly little indeed. When I
+realized it, I tried hard to keep intact the great performance of `EnTT` and to
+add all the features I wanted to see in *my* entity-component system at the same
+time.
 
-### Performance
+Today `EnTT` is finally what I was looking for: still faster than its _rivals_,
+a really good API and an amazing set of features. And even more, of course.
 
-As it stands right now, `EnTT` is just fast enough for my requirements if compared to my first choice (that was already
-amazingly fast).
-These are the results of the twos when compiled with GCC 6.3:
+## Performance
+
+As it stands right now, `EnTT` is just fast enough for my requirements if
+compared to my first choice (that was already amazingly fast indeed).<br/>
+Here is a comparision between the two (both of them compiled with GCC 7.2.0 on a
+Dell XPS 13 out of the mid 2014):
 
 | Benchmark | EntityX (experimental/compile_time) | EnTT |
 |-----------|-------------|-------------|
-| Creating 10M entities | 0.187042s | **0.0928331s** |
-| Destroying 10M entities | 0.0735151s | **0.060166s** |
-| Iterating over 10M entities, unpacking one component | 0.00784801s | **1.02e-07s** |
-| Iterating over 10M entities, unpacking two components | 0.00865273s | **0.00326714s** |
-| Iterating over 10M entities, unpacking five components | 0.0122006s | **0.00323354s** |
-| Iterating over 10M entities, unpacking ten components | 0.0100089s | **0.00323615s** |
-| Iterating over 50M entities, unpacking one component | 0.0394404s | **1.14e-07s** |
-| Iterating over 50M entities, unpacking two components | 0.0400407s | **0.0179783s** |
+| Creating 10M entities | 0.128881s | **0.0408754s** |
+| Destroying 10M entities | **0.0531374s** | 0.0545839s |
+| Iterating over 10M entities, unpacking one component, standard view | 0.010661s | **1.58e-07s** |
+| Iterating over 10M entities, unpacking two components, standard view | **0.0112664s** | 0.0840068s |
+| Iterating over 10M entities, unpacking two components, standard view, half of the entities have all the components | **0.0077951s** | 0.042168s |
+| Iterating over 10M entities, unpacking two components, standard view, one of the entities has all the components | 0.00713398s | **8.93e-07s** |
+| Iterating over 10M entities, unpacking two components, persistent view | 0.0112664s | **5.68e-07s** |
+| Iterating over 10M entities, unpacking five components, standard view | **0.00905084s** | 0.137757s |
+| Iterating over 10M entities, unpacking five components, persistent view | 0.00905084s | **2.9e-07s** |
+| Iterating over 10M entities, unpacking ten components, standard view | **0.0104708s** | 0.388602s |
+| Iterating over 10M entities, unpacking ten components, standard view, half of the entities have all the components | **0.00899859s** | 0.200752s |
+| Iterating over 10M entities, unpacking ten components, standard view, one of the entities has all the components | 0.00700349s | **2.565e-06s** |
+| Iterating over 10M entities, unpacking ten components, persistent view | 0.0104708s | **6.23e-07s** |
+| Iterating over 50M entities, unpacking one component, standard view | 0.055194s | **2.87e-07s** |
+| Iterating over 50M entities, unpacking two components, standard view | **0.0533921s** | 0.243197s |
+| Iterating over 50M entities, unpacking two components, persistent view | 0.055194s | **4.47e-07s** |
+| Sort 150k entities, one component | - | **0.0080046s** |
+| Sort 150k entities, match two components | - | **0.00608322s** |
 
-These are the results of the twos when compiled with Clang 3.8.1:
+`EnTT` includes its own tests and benchmarks. See
+[benchmark.cpp](https://github.com/skypjack/entt/blob/master/test/benchmark.cpp)
+for further details.<br/>
+On Github users can find also a
+[benchmark suite](https://github.com/abeimler/ecs_benchmark) that compares a
+bunch of different projects, one of which is `EnTT`.
 
-| Benchmark | EntityX (experimental/compile_time) | EnTT |
-|-----------|-------------|-------------|
-| Creating 10M entities | 0.268049s | **0.0899998s** |
-| Destroying 10M entities | **0.0713912s** | 0.078663s |
-| Iterating over 10M entities, unpacking one component | 0.00863192s | **3.05e-07s** |
-| Iterating over 10M entities, unpacking two components | 0.00780158s | **2.5434e-05s** |
-| Iterating over 10M entities, unpacking five components | 0.00829669s | **2.5497e-05s** |
-| Iterating over 10M entities, unpacking ten components | 0.00789789s | **2.5563e-05s** |
-| Iterating over 50M entities, unpacking one component | 0.0423244s | **1.94e-07s** |
-| Iterating over 50M entities, unpacking two components | 0.0435464s | **0.00012661s** |
-
-I don't know what Clang does to squeeze out of `EnTT` the performance above, but I'd say that it does it incredibly well.
-
-See [benchmark.cpp](https://github.com/skypjack/entt/blob/master/test/benchmark.cpp) for further details.<br/>
-Of course, I'll try to get out of it more features and better performance anyway in the future, mainly for fun.
-If you want to contribute and have any suggestion, feel free to make a PR or open an issue to discuss them.
-
-### Benchmarks / Comparisons
-
-`EnTT` includes its own benchmarks, mostly similar to the ones of `EntityX` so as to compare them.<br/>
-On Github you can find also a [benchmark suite](https://github.com/abeimler/ecs_benchmark) testing `EntityX` (both the official version and the compile-time one), `Anax` and `Artemis C++` with up to 10M entities.
+Of course, probably I'll try to get out of `EnTT` more features and better
+performance in the future, mainly for fun.<br/>
+If you want to contribute and/or have any suggestion, feel free to make a PR or
+open an issue to discuss your idea.
 
 # Build Instructions
 
 ## Requirements
 
-To be able to use `EnTT`, users must provide a full-featured compiler that supports at least C++14.<br/>
-CMake version 3.4 or later is mandatory to compile the tests, you don't have to install it otherwise.
+To be able to use `EnTT`, users must provide a full-featured compiler that
+supports at least C++14.<br/>
+The requirements below are mandatory to compile the tests and to extract the
+documentation:
+
+* CMake version 3.2 or later.
+* Doxygen version 1.8 or later.
 
 ## Library
 
-`EnTT` is a header-only library. This means that including the `registry.hpp` header is enough to use it.<br/>
-It's a matter of adding the following line at the top of a file:
+`EnTT` is a header-only library. This means that including the `entt.hpp`
+header is enough to include the whole framework and use it. For those who are
+interested only in the entity-component system, consider to include the sole
+`entity/registry.hpp` header instead.<br/>
+It's a matter of adding the following line to the top of a file:
 
 ```cpp
-#include <registry.hpp>
+#include <entt/entt.hpp>
 ```
 
-Then pass the proper `-I` argument to the compiler to add the `src` directory to the include paths.<br/>
+Use the line below to include only the entity-component system instead:
+
+```cpp
+#include <entt/entity/registry.hpp>
+```
+
+Then pass the proper `-I` argument to the compiler to add the `src` directory to
+the include paths.
 
 ## Documentation
 
-### API Reference
+The documentation is based on [doxygen](http://www.stack.nl/~dimitri/doxygen/).
+To build it:
 
-`EnTT` contains three main actors: the *registry*, the *view* and the *pool*.<br/>
-Unless you have specific requirements of memory management, the default registry (that used the pool provided with
-`EnTT`) should be good enough for any use. Customization is an option anyway, so that you can use your own pool as
-long as it offers the expected interface.
+    $ cd build
+    $ cmake ..
+    $ make docs
 
-#### The Registry
+The API reference will be created in HTML format within the directory
+`build/docs/html`. To navigate it with your favorite browser:
 
-There are three options to instantiate your own registry:
+    $ cd build
+    $ your_favorite_browser docs/html/index.html
 
-* By using the default one:
-
-    ```cpp
-    auto registry = entt::DefaultRegistry<Components...>{args...};
-    ```
-
-  That is, you must provide the whole list of components to be registered with the default registry.
-
-* By using the standard one:
-
-    ```cpp
-    auto registry = entt::StandardRegistry<std::uint16_t, Components...>{args...};
-    ```
-
-  That is, you must provide the whole list of components to be registered with the default registry **and** the desired type for the entities. Note that the default type is `std::uint32_t`, that is larger enough for almost all the games but also too big for the most of the games.
-
-* By using your own pool:
-
-    ```cpp
-    auto registry = entt::Registry<DesiredEntityType, YourOwnPool<Components...>>{args...};
-    ```
-
-  Note that the registry expects a class template where the template parameters are the components to be managed.
-
-In both cases, `args...` parameters are forwarded to the underlying pool during the construction.<br/>
-There are no requirements for the components but to be moveable, therefore POD types are just fine.
-
-Once you have created a registry, the followings are the exposed member functions:
-
-* `size`: returns the number of entities still alive.
-* `capacity`: returns the maximum number of entities created till now.
-* `valid`: returns true if the entity is still in use, false otherwise.
-* `empty<Component>`: returns `true` if at least an instance of `Component` exists, `false` otherwise.
-* `empty`: returns `true` if all the entities have been destroyed, `false` otherwise.
-* `create<Components...>`: creates a new entity and assigns it the given components, then returns the entity.
-* `create`: creates a new entity and returns it, no components assigned.
-* `destroy`: destroys the entity and all its components.
-* `assign<Component>(entity, args...)`: assigns the given component to the entity and uses `args...` to initialize it.
-* `remove<Component>(entity)`: removes the given component from the entity.
-* `has<Components...>(entity)`: returns `true` if the entity has the given components, `false` otherwise.
-* `get<Component>(entity)`: returns a reference to the given component for the entity (undefined behaviour if the entity has not the component).
-* `replace<Component>(entity, args...)`: replaces the given component for the entity, using `args...` to create the new component.
-* `accomodate<Component>(entity, args...)`: replaces the given component for the entity if it exists, otherwise assigns it to the entity and uses `args...` to initialize it.
-* `clone(entity)`: clones an entity and all its components, then returns the new entity identifier.
-* `copy<Component>(to, from)`: copies a component from an entity to another one (both the entities must already have been assigned the component, undefined behaviour otherwise).
-* `copy(to, from)`: copies all the components and their contents from an entity to another one (comoonents are created or destroyed if needed).
-* `reset<Component>(entity)`: removes the given component from the entity if assigned.
-* `reset<Component>()`: destroys all the instances of `Component`.
-* `reset()`: resets the pool and destroys all the entities and their components.
-* `view<Components...>()`: gets a view of the entities that have the given components (see below for further details).
-
-Note that entities are numbers and nothing more. They are not classes and they have no member functions at all.
-
-#### The View
-
-There are three different kinds of view, each one with a slighlty different interface:
-
-* The _single component view_.
-* The _multi component view_.
-
-All of them are iterable. In other terms they have `begin` and `end` member functions that are suitable for a range-based for loop:
-
-```cpp
-auto view = registry.view<Position, Velocity>();
-
-for(auto entity: view) {
-    // do whatever you want with your entities
-}
-```
-
-Iterators are extremely poor, they are meant exclusively to be used to iterate over a set of entities.<br/>
-Guaranteed exposed member functions are:
-
-* `operator++()`
-* `operator++(int)`
-* `operator==()`
-* `operator!=()`
-* `operator*()`
-
-The single component view has an additional member function:
-
-* `size()`: returns the exact number of expected entities.
-
-The multi component view has an additional member function:
-
-* `reset()`: reorganizes internal data so as to further create optimized iterators (use it whenever the data within the registry are known to be changed).
-
-All the views can be used more than once. They return newly created and correctly initialized iterators whenever
-`begin` or `end` is invoked. Anyway views and iterators are tiny objects and the time to construct them can be safely ignored.
-I'd suggest not to store them anywhere and to invoke the `Registry::view` member function at each iteration to get a properly
-initialized view over which to iterate.
-
-**Note**: If underlying sets are modified, iterators are invalidated and using them is undefined behaviour.<br/>
-Do not try to assign or remove components on which you are iterating to entities. There are no guarantees.
-
-**Note**: Iterators aren't thread safe. Do no try to iterate over a set of components and modify them concurrently.
-That being said, as long as a thread iterates over the entities that have the component `X` or assign and removes
-that component from a set of entities and another thread does something similar with components `Y` and `Z`, it shouldn't be a
-problem at all.<br/>
-As an example, that means that users can freely run the rendering system over the renderable entities and update the physics
-concurrently on a separate thread if needed.
-
-#### The Pool
-
-Custom pools for a given component can be defined as a specialization of the class template `ComponentPool`.<br/>
-In particular:
-
-```cpp
-template<>
-struct ComponentPool<Entity, MyComponent> final {
-    // ...
-};
-```
-
-Where `Entity` is the desired type for the entities, `MyComponent` the type of the component to be stored.
-
-A custom pool should expose at least the following member functions:
-
-* `bool empty() const noexcept;`
-* `size_type capacity() const noexcept;`
-* `size_type size() const noexcept;`
-* `iterator_type begin() noexcept;`
-* `const_iterator_type begin() const noexcept;`
-* `iterator_type end() noexcept;`
-* `const_iterator_type end() const noexcept;`
-* `bool has(entity_type entity) const noexcept;`
-* `const component_type & get(entity_type entity) const noexcept;`
-* `component_type & get(entity_type entity) noexcept;`
-* `template<typename... Args> component_type & construct(entity_type entity, Args... args);`
-* `void destroy(entity_type entity);`
-* `void reset();`
-
-This is a fast and easy way to define a custom pool specialization for a given component (as an example, if the
-component `X` requires to be ordered internally somehow during construction or destruction operations) and to use the
-default pool for all the other components.<br/>
-It's a mattrer of including the given specialization along with the registry, so that it can find it during the instantiation.<br/>
-In this case, users are not required to use the more explicit `Registry` class. Instead, they can still use `entt::DefaultRegistry`.
-
-In cases when the per-component pools are not good enough, the registry can be initialized with a custom pool.<br/>
-In other terms, `entt::Registry` has a template template parameter that can be used to provide both the pool and the list of
-components:
-
-```cpp
-auto registry = entt::Registry<Entity, MyCustomPool<Component1, Component2>>{};
-```
-
-Even though the underlying pool doesn't store the components separately, the registry must know them to be able to do
-specific actions (like `destroy` or `copy`). That's why they must be explicitly specified.<br/>
-A generic pool should expose at least the following memeber functions:
-
-* `template<typename Component> bool empty() const noexcept;`
-* `template<typename Component> size_type capacity() const noexcept;`
-* `template<typename Component> size_type size() const noexcept;`
-* `template<typename Component> iterator_type begin() noexcept;`
-* `template<typename Component> const_iterator_type begin() const noexcept;`
-* `template<typename Component> iterator_type end() noexcept;`
-* `template<typename Component> const_iterator_type end() const noexcept;`
-* `template<typename Component> bool has(entity_type entity) const noexcept;`
-* `template<typename Component> const Comp & get(entity_type entity) const noexcept;`
-* `template<typename Component> Comp & get(entity_type entity) noexcept;`
-* `template<typename Component, typename... Args> Comp & construct(entity_type entity, Args... args);`
-* `template<typename Component> void destroy(entity_type entity);`
-* `template<typename Component> void reset();`
-* `void reset();`
-
-Good luck. If you come out with a more performant components pool, do not forget to make a PR so that I can add it to
-the list of available ones. I would be glad to have such a contribution to the project!!
+The API reference is also available [online](https://skypjack.github.io/entt/)
+for the latest version.
 
 ## Tests
 
 To compile and run the tests, `EnTT` requires *googletest*.<br/>
-Run the script `deps.sh` to download it. It is good practice to do it every time one pull the project.
+`cmake` will download and compile the library before to compile anything else.
 
-Then, to build the tests:
+To build the tests:
 
 * `$ cd build`
 * `$ cmake ..`
 * `$ make`
 * `$ make test`
 
+To build the benchmarks, use the following line instead:
+
+* `$ cmake -DCMAKE_BUILD_TYPE=Release ..`
+
+Benchmarks are compiled only in release mode currently.
+
+# Crash Course
+
+## Vademecum
+
+The `Registry` to store, the `View`s to iterate. That's all.
+
+An entity (the _E_ of an _ECS_) is an opaque identifier that users should just
+use as-is and store around if needed. Do not try to inspect an entity
+identifier, its type can change in future and a registry offers all the
+functionalities to query them out-of-the-box. The underlying type of an entity
+(either `std::uint16_t`, `std::uint32_t` or `std::uint64_t`) can be specified
+when defining a registry (actually the DefaultRegistry is nothing more than a
+Registry where the type of the entities is `std::uint32_t`).<br/>
+Components (the _C_ of an _ECS_) should be plain old data structures or more
+complex and moveable data structures with a proper constructor. They are list
+initialized by using the parameters provided to construct the component. No need
+to register components or their types neither with the registry nor with the
+entity-component system at all.<br/>
+Systems (the _S_ of an _ECS_) are just plain functions, functors, lambdas or
+whatever the users want. They can accept a Registry, a View or a PersistentView
+and use them the way they prefer. No need to register systems or their types
+neither with the registry nor with the entity-component system at all.
+
+The following sections will explain in short how to use the entity-component
+system, the core part of the `EnTT` framework.<br/>
+In fact, the framework is composed of many other classes in addition to those
+describe below. For more details, please refer to the
+[online documentation](https://skypjack.github.io/entt/).
+
+## The Registry, the Entity and the Component
+
+A registry is used to store and manage entities as well as to create views to
+iterate the underlying data structures.<br/>
+Registry is a class template that lets the users decide what's the preferred
+type to represent an entity. Because `std::uint32_t` is large enough for almost
+all the cases, there exists also an alias named DefaultRegistry for
+`Registry<std::uint32_t>`.
+
+Entities are represented by _entitiy identifiers_. An entity identifier is an
+opaque type that users should not inspect or modify in any way. It carries
+information about the entity itself and its version.
+
+A registry can be used both to construct and to destroy entities:
+
+```cpp
+// constructs a naked entity with no components ad returns its identifier
+auto entity = registry.create();
+
+// constructs an entity and assigns it default-initialized components
+auto another = registry.create<Position, Velocity>();
+
+// destroys an entity and all its components
+registry.destroy(entity);
+```
+
+Once an entity is deleted, the registry can freely reuse it internally with a
+slightly different identifier. In particular, the version of an entity is
+increased each and every time it's destroyed.<br/>
+In case entity identifiers are stored around, the registry offers all the
+functionalities required to test them and get out of the them all the
+information they carry:
+
+```cpp
+// returns true if the entity is still valid, false otherwise
+bool b = registry.valid(entity);
+
+// gets the version contained in the entity identifier
+auto version = registry.version(entity);
+
+// gets the actual version for the given entity
+auto curr = registry.current(entity);
+```
+
+Components can be assigned to or removed from entities at any time with a few
+calls to member functions of the registry. As for the entities, the registry
+offers also a set of functionalities users can use to work with the components.
+
+The `assign` member function template creates, initializes and assigns to an
+entity the given component. It accepts a variable number of arguments that are
+used to construct the component itself if present:
+
+```cpp
+registry.assign<Position>(entity, 0., 0.);
+
+// ...
+
+auto &velocity = registry.assign<Velocity>(entity);
+velocity.dx = 0.;
+velocity.dy = 0.;
+```
+
+If the entity already has the given component, the `replace` member function
+template can be used to replace it:
+
+```cpp
+registry.replace<Position>(entity, 0., 0.);
+
+// ...
+
+auto &velocity = registry.replace<Velocity>(entity);
+velocity.dx = 0.;
+velocity.dy = 0.;
+```
+
+In case users want to assign a component to an entity, but it's unknown whether
+the entity already has it or not, `accomodate` does the work in a single call
+(of course, there is a performance penalty to pay for that mainly due to the
+fact that it must check if `entity` already has the given component or not):
+
+```cpp
+registry.accomodate<Position>(entity, 0., 0.);
+
+// ...
+
+auto &velocity = registry.accomodate<Velocity>(entity);
+velocity.dx = 0.;
+velocity.dy = 0.;
+```
+
+Note that `accomodate` is a sliglhty faster alternative for the following
+`if`/`else` statement and nothing more:
+
+```cpp
+if(registry.has<Comp>(entity)) {
+    registry.replace<Comp>(entity, arg1, argN);
+} else {
+    registry.assign<Comp>(entity, arg1, argN);
+}
+```
+
+As already shown, if in doubt about whether or not an entity has one or more
+components, the `has` member function template may be useful:
+
+```cpp
+bool b = registry.has<Position, Velocity>(entity);
+```
+
+On the other side, if the goal is to delete a single component, the `remove`
+member function template is the way to go when it's certain that the entity owns
+a copy of the component:
+
+```cpp
+registry.remove<Position>(entity);
+```
+
+Otherwise consider to use the `reset` member function. It behaves similarly to
+`remove` but with a strictly defined behaviour (and a performance penalty is the
+price to pay for that). In particular it removes the component if and only if it
+exists, otherwise it returns safely to the caller:
+
+```cpp
+registry.reset<Position>(entity);
+```
+
+There exist also two other _versions_ of the `reset` member function:
+
+* If no entity is passed to it, `reset` will remove the given component from
+each entity that has it:
+
+  ```cpp
+  registry.reset<Position>();
+  ```
+
+* If neither the entity nor the component are specified, all the entities and
+their components are destroyed:
+
+  ```cpp
+  registry.reset();
+  ```
+
+Finally, references to components can be retrieved by just doing this:
+
+```cpp
+// either a non-const reference ...
+DefaultRegistry registry;
+auto &position = registry.get<Position>(entity);
+
+// ... or a const one
+const auto &cregistry = registry;
+const auto &position = cregistry.get<Position>(entity);
+```
+
+The `get` member function template gives direct access to the component of an
+entity stored in the underlying data structures of the registry.
+
+### Sorting: is it possible?
+
+Of course, sorting entities and components is possible with `EnTT`.<br/>
+In fact, there are two functions that respond to slightly different needs:
+
+* Components can be sorted directly:
+
+  ```cpp
+  registry.sort<Renderable>([](const auto &lhs, const auto &rhs) {
+      return lhs.z < rhs.z;
+  });
+  ```
+
+* Components can be sorted according to the order imposed by another component:
+
+  ```cpp
+  registry.sort<Movement, Physics>();
+  ```
+
+  In this case, instances of `Movement` are arranged in memory so that cache
+  misses are minimized when the two components are iterated together.
+
+## View: to persist or not to persist?
+
+There are mainly two kinds of views: standard (also known as View) and
+persistent (alsa known as PersistentView).<br/>
+Both of them have pros and cons to take in consideration. In particular:
+
+* Standard views:
+
+  Pros:
+  * They work out-of-the-box and don't require any dedicated data
+    structure.
+  * Creating and destroying them isn't expensive at all because they don't
+    have any type of initialization.
+  * They are the best tool to iterate single components.
+  * They are the best tool to iterate multiple components at once when
+    tags are involved or one of the component is assigned to a
+    significantly low number of entities.
+  * They don't affect any other operations of the registry.
+
+  Cons:
+  * Their performance tend to degenerate when the number of components
+    to iterate grows up and the most of the entities have all of them.
+
+* Persistent views:
+
+  Pros:
+  * Once prepared, creating and destroying them isn't expensive at all
+    because they don't have any type of initialization.
+  * They are the best tool to iterate multiple components at once when
+    the most of the entities have all of them.
+
+  Cons:
+    * They have dedicated data structures and thus affect the memory
+      pressure to a minimal extent.
+    * If not previously prepared, the first time they are used they go
+      through an initialization step that could take a while.
+    * They affect to a minimum the creation and destruction of entities and
+      components. In other terms: the more persistent views there will be,
+      the less performing will be creating and destroying entities and
+      components.
+
+To sum up and as a rule of thumb, use a standard view:
+* To iterate entities for a single component.
+* To iterate entities for multiple components when a significantly low
+  number of entities have one of the components.
+* In all those cases where a persistent view would give a boost to
+  performance but the iteration isn't performed frequently.
+
+Use a persistent view in all the other cases.
+
+To easily iterate entities, all the views offer _C++-ish_ `begin` and `end`
+member functions that allow users to use them in a typical range-for loop.<br/>
+Continue reading for more details or refer to the
+[official documentation](https://skypjack.github.io/entt/).
+
+### Standard View
+
+A standard view behaves differently if it's constructed for a single component
+or if it has been requested to iterate multiple components. Even the API is
+different in the two cases.<br/>
+All that they share is the way they are created by means of a registry:
+
+```cpp
+// single component standard view
+auto single = registry.view<Position>();
+
+// multi component standard view
+auto multi = registry.view<Position, Velocity>();
+```
+
+For all that remains, it's worth discussing them separately.<br/>
+
+#### Single component standard view
+
+Single component standard views are specialized in order to give a boost in
+terms of performance in all the situation. This kind of views can access the
+underlying data structures directly and avoid superflous checks.<br/>
+They offer a bunch of functionalities to get the number of entities they are
+going to return and a raw access to the entity list as well as to the component
+list.<br/>
+Refer to the [official documentation](https://skypjack.github.io/entt/) for all
+the details.
+
+There is no need to store views around for they are extremely cheap to
+construct, even though they can be copied without problems and reused
+freely. In fact, they return newly created and correctly initialized iterators
+whenever `begin` or `end` are invoked.<br/>
+To iterate a single component standard view, just use it in range-for:
+
+```cpp
+auto view = registry.view<Renderable>();
+
+for(auto entity: view) {
+    auto &renderable = view.get(entity);
+
+    // ...
+}
+```
+
+**Note**: prefer the `get` member function of the view instead of the `get`
+member function template of the registry during iterations.
+
+#### Multi component standard view
+
+Multi component standard views iterate entities that have at least all the given
+components in their bags. During construction, these views look at the number
+of entities available for each component and pick up a reference to the smallest
+set of candidates in order to speed up iterations.<br/>
+They offer fewer functionalities than their companion views for single
+component, the most important of which can be used to reset the view and refresh
+the reference to the set of candidate entities to iterate.<br/>
+Refer to the [official documentation](https://skypjack.github.io/entt/) for all
+the details.
+
+There is no need to store views around for they are extremely cheap to
+construct, even though they can be copied without problems and reused
+freely. In fact, they return newly created and correctly initialized iterators
+whenever `begin` or `end` are invoked.<br/>
+To iterate a multi component standard view, just use it in range-for:
+
+```cpp
+auto view = registry.view<Position, Velocity>();
+
+for(auto entity: view) {
+    auto &position = view.get<Position>(entity);
+    auto &velocity = view.get<Velocity>(entity);
+
+    // ...
+}
+```
+
+**Note**: prefer the `get` member function template of the view instead of the
+`get` member function template of the registry during iterations.
+
+### Persistent View
+
+A persistent view returns all the entities and only the entities that have at
+least the given components. Moreover, it's guaranteed that the entity list is
+thightly packed in memory for fast iterations.<br/>
+In general, persistent views don't stay true to the order of any set of
+components unless users explicitly sort them.
+
+Persistent views can be used only to iterate multiple components. Create them
+as it follows:
+
+```cpp
+auto view = registry.persistent<Position, Velocity>();
+```
+
+There is no need to store views around for they are extremely cheap to
+construct, even though they can be copied without problems and reused
+freely. In fact, they return newly created and correctly initialized iterators
+whenever `begin` or `end` are invoked.<br/>
+That being said, persistent views perform an initialization step the very first
+time they are constructed and this could be quite costly. To avoid it, consider
+asking to the registry to _prepare_ them when no entities have been created yet:
+
+```cpp
+registry.prepare<Position, Velocity>();
+```
+
+If the registry is empty, preparation is extremely fast. Moreover the `prepare`
+member function template is idempotent. Feel free to invoke it even more than
+once: if the view has been alreadt prepared before, the function returns
+immediately and does nothing.
+
+A persistent view offers a bunch of functionalities to get the number of
+entities it's going to return, a raw access to the entity list and the
+possibility to sort the underlying data structures according to the order of one
+of the components for which it has been constructed.<br/>
+Refer to the [official documentation](https://skypjack.github.io/entt/) for all
+the details.
+
+To iterate a persistent view, just use it in range-for:
+
+```cpp
+auto view = registry.persistent<Position, Velocity>();
+
+for(auto entity: view) {
+    auto &position = view.get<Position>(entity);
+    auto &velocity = view.get<Velocity>(entity);
+
+    // ...
+}
+```
+
+**Note**: prefer the `get` member function template of the view instead of the
+`get` member function template of the registry during iterations.
+
+## Side notes
+
+* Entity identifiers are numbers and nothing more. They are not classes and they
+  have no member functions at all. As already mentioned, do no try to inspect or
+  modify an entity descriptor in any way.
+
+* As shown in the examples above, the preferred way to get references to the
+  components while iterating a view is by using the view itself. It's a faster
+  alternative to the `get` member function template that is part of the API of
+  the Registry. That's because the registry must ensure that a pool for the
+  given component exists before to use it; on the other side, views force the
+  construction of the pools for all their components and access them directly,
+  thus avoiding all the checks.
+
+* Most of the _ECS_ available out there have an annoying limitation (at least
+  from my point of view): entities and components cannot be created and/or
+  deleted during iterations.<br/>
+  `EnTT` partially solves the problem with a few limitations:
+
+  * Creating entities and components is allowed during iterations.
+  * Deleting an entity or removing its components is allowed during
+    iterations if it's the one currently returned by a view. For all the
+    other entities, destroying them or removing their components isn't
+    allowed and it can result in undefined behavior.
+
+  Iterators are invalidated and the behaviour is undefined if an entity is
+  modified or destroyed and it's not the one currently returned by the
+  view.<br/>
+  To work around it, possible approaches are:
+
+    * Store aside the entities and the components to be removed and perform the
+      operations at the end of the iteration.
+    * Mark entities and components with a proper tag component that indicates
+      they must be purged, then perform a second iteration to clean them up one
+      by one.
+
+* Views and thus their iterators aren't thread safe. Do no try to iterate a set
+  of components and modify the same set concurrently.<br/>
+  That being said, as long as a thread iterates the entities that have the
+  component `X` or assign and removes that component from a set of entities,
+  another thread can safely do the same with components `Y` and `Z` and
+  everything will work like a charm.<br/>
+  As an example, users can freely execute the rendering system and iterate the
+  renderable entities while updating a physic component concurrently on a
+  separate thread if needed.
+
+## What else?
+
+The `EnTT` framework is moving its first steps. More and more will come in the
+future and hopefully I'm going to work on it for a long time.<br/>
+Here is a brief list of what it offers today:
+
+* Statically generated integer identifiers for types.
+* An entity-component system based on sparse sets.
+* Signal handlers and event emitters of any type.
+* ...
+* Any other business.
+
+Consider it a work in progress. For more details and an updated list, please
+refer to the [online documentation](https://skypjack.github.io/entt/).
+
 # Contributors
 
-If you want to contribute, please send patches as pull requests against the branch master.<br/>
-Check the [contributors list](https://github.com/skypjack/entt/blob/master/AUTHORS) to see who has partecipated so far.
+If you want to contribute, please send patches as pull requests against the
+branch `master`.<br/>
+Check the
+[contributors list](https://github.com/skypjack/entt/blob/master/AUTHORS) to see
+who has partecipated so far.
 
 # License
 
 Code and documentation Copyright (c) 2017 Michele Caini.<br/>
-Code released under [the MIT license](https://github.com/skypjack/entt/blob/master/LICENSE).
+Code released under
+[the MIT license](https://github.com/skypjack/entt/blob/master/LICENSE).
+Docs released under
+[Creative Commons](https://github.com/skypjack/entt/blob/master/docs/LICENSE).
+
+# Donation
+
+Developing and maintaining `EnTT` takes some time and lots of coffee. I'd like
+to add more and more functionalities in future and turn it in a full-featured
+framework.<br/>
+If you want to support this project, you can offer me an espresso. I'm from
+Italy, we're used to turning the best coffee ever in code. If you find that
+it's not enough, feel free to support me the way you prefer.<br/>
+Take a look at the donation button at the top of the page for more details or
+just click [here](https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=W2HF9FESD5LJY&lc=IT&item_name=Michele%20Caini&currency_code=EUR&bn=PP%2dDonationsBF%3abtn_donateCC_LG%2egif%3aNonHosted).

appveyor.yml

@@ -1,7 +1,7 @@
 # can use variables like {build} and {branch}
 version: 1.0.{build}
 
-image: Visual Studio 2015
+image: Visual Studio 2017
 
 environment:
   BUILD_DIR: "%APPVEYOR_BUILD_FOLDER%\\build"
@@ -13,9 +13,8 @@ configuration:
   - Release
 
 before_build:
-  - deps.bat
   - cd %BUILD_DIR%
-  - cmake .. -G"%CMAKE_GENERATOR_NAME%"
+  - cmake .. -G"Visual Studio 15 2017"
 
 build:
   parallel: true

cmake/in/googletest.in

@@ -6,7 +6,7 @@ include(ExternalProject)
 ExternalProject_Add(
     googletest
     GIT_REPOSITORY https://github.com/google/googletest.git
-    GIT_TAG master
+    GIT_TAG release-1.8.0
     DOWNLOAD_DIR ${GOOGLETEST_DEPS_DIR}
     TMP_DIR ${GOOGLETEST_DEPS_DIR}/tmp
     STAMP_DIR ${GOOGLETEST_DEPS_DIR}/stamp

docs/CMakeLists.txt

@@ -0,0 +1,27 @@
+#
+# Doxygen configuration (documentation)
+#
+
+set(TARGET_DOCS docs)
+
+set(DOXY_IN_FILE doxy.in)
+
+set(DOXY_SOURCE_DIRECTORY ${PROJECT_SRC_DIR})
+set(DOXY_DOCS_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR})
+set(DOXY_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
+set(DOXY_CFG_FILE doxy.cfg)
+
+configure_file(${DOXY_IN_FILE} ${DOXY_CFG_FILE} @ONLY)
+
+add_custom_target(
+    ${TARGET_DOCS}
+    COMMAND ${DOXYGEN_EXECUTABLE} ${CMAKE_CURRENT_BINARY_DIR}/${DOXY_CFG_FILE}
+    WORKING_DIRECTORY ${entt_SOURCE_DIR}
+    VERBATIM
+    SOURCES ${DOXY_IN_FILE}
+)
+
+install(
+    DIRECTORY ${DOXY_OUTPUT_DIRECTORY}/html
+    DESTINATION share/${PROJECT_NAME}-${PROJECT_VERSION}/
+)

docs/LICENSE

@@ -0,0 +1,395 @@
+Attribution 4.0 International
+
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+
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docs/extra.dox

@@ -0,0 +1,5 @@
+/**
+ * @namespace entt
+ *
+ * @brief `EnTT` default namespace.
+ */

src/component_pool.hpp

@@ -1,235 +0,0 @@
-#ifndef ENTT_COMPONENT_POOL_HPP
-#define ENTT_COMPONENT_POOL_HPP
-
-
-#include <utility>
-#include <vector>
-#include <cassert>
-
-
-namespace entt {
-
-
-template<typename, typename, typename...>
-class ComponentPool;
-
-
-template<typename Entity, typename Component>
-class ComponentPool<Entity, Component> {
-public:
-    using component_type = Component;
-    using entity_type = Entity;
-    using pos_type = entity_type;
-    using size_type = typename std::vector<component_type>::size_type;
-    using iterator_type = typename std::vector<entity_type>::iterator;
-    using const_iterator_type = typename std::vector<entity_type>::const_iterator;
-
-private:
-    inline bool valid(entity_type entity) const noexcept {
-        return entity < reverse.size() && reverse[entity] < direct.size() && direct[reverse[entity]] == entity;
-    }
-
-public:
-    explicit ComponentPool(size_type dim = 4098) noexcept {
-        assert(!(dim < 0));
-        data.reserve(dim);
-    }
-
-    ComponentPool(ComponentPool &&) = default;
-
-    ~ComponentPool() noexcept {
-        assert(empty());
-    }
-
-    ComponentPool & operator=(ComponentPool &&) = default;
-
-    bool empty() const noexcept {
-        return data.empty();
-    }
-
-    size_type capacity() const noexcept {
-        return data.capacity();
-    }
-
-    size_type size() const noexcept {
-        return data.size();
-    }
-
-    iterator_type begin() noexcept {
-        return direct.begin();
-    }
-
-    const_iterator_type cbegin() const noexcept {
-        return direct.cbegin();
-    }
-
-    iterator_type end() noexcept {
-        return direct.end();
-    }
-
-    const_iterator_type cend() const noexcept {
-        return direct.cend();
-    }
-
-    bool has(entity_type entity) const noexcept {
-        return valid(entity);
-    }
-
-    const component_type & get(entity_type entity) const noexcept {
-        assert(valid(entity));
-        return data[reverse[entity]];
-    }
-
-    component_type & get(entity_type entity) noexcept {
-        return const_cast<component_type &>(const_cast<const ComponentPool *>(this)->get(entity));
-    }
-
-    template<typename... Args>
-    component_type & construct(entity_type entity, Args... args) {
-        assert(!valid(entity));
-
-        if(!(entity < reverse.size())) {
-            reverse.resize(entity+1);
-        }
-
-        reverse[entity] = pos_type(direct.size());
-        direct.emplace_back(entity);
-        data.push_back({ args... });
-
-        return data.back();
-    }
-
-    void destroy(entity_type entity) {
-        assert(valid(entity));
-
-        auto last = direct.size() - 1;
-
-        reverse[direct[last]] = reverse[entity];
-        direct[reverse[entity]] = direct[last];
-        data[reverse[entity]] = std::move(data[last]);
-
-        direct.pop_back();
-        data.pop_back();
-    }
-
-    void reset() {
-        data.clear();
-        reverse.resize(0);
-        direct.clear();
-    }
-
-private:
-    std::vector<component_type> data;
-    std::vector<pos_type> reverse;
-    std::vector<entity_type> direct;
-};
-
-
-template<typename Entity, typename Component, typename... Components>
-class ComponentPool
-        : ComponentPool<Entity, Component>, ComponentPool<Entity, Components>...
-{
-    template<typename Comp>
-    using Pool = ComponentPool<Entity, Comp>;
-
-public:
-    using entity_type = typename Pool<Component>::entity_type;
-    using pos_type = typename Pool<Component>::pos_type;
-    using size_type = typename Pool<Component>::size_type;
-    using iterator_type = typename Pool<Component>::iterator_type;
-    using const_iterator_type = typename Pool<Component>::const_iterator_type;
-
-    explicit ComponentPool(size_type dim = 4098) noexcept
-#ifdef _MSC_VER
-        : ComponentPool<Entity, Component>{dim}, ComponentPool<Entity, Components>{dim}...
-#else
-        : Pool<Component>{dim}, Pool<Components>{dim}...
-#endif
-    {
-        assert(!(dim < 0));
-    }
-
-    ComponentPool(const ComponentPool &) = delete;
-    ComponentPool(ComponentPool &&) = delete;
-
-    ComponentPool & operator=(const ComponentPool &) = delete;
-    ComponentPool & operator=(ComponentPool &&) = delete;
-
-    template<typename Comp>
-    bool empty() const noexcept {
-        return Pool<Comp>::empty();
-    }
-
-    template<typename Comp>
-    size_type capacity() const noexcept {
-        return Pool<Comp>::capacity();
-    }
-
-    template<typename Comp>
-    size_type size() const noexcept {
-        return Pool<Comp>::size();
-    }
-
-    template<typename Comp>
-    iterator_type begin() noexcept {
-        return Pool<Comp>::begin();
-    }
-
-    template<typename Comp>
-    const_iterator_type cbegin() const noexcept {
-        return Pool<Comp>::cbegin();
-    }
-
-    template<typename Comp>
-    iterator_type end() noexcept {
-        return Pool<Comp>::end();
-    }
-
-    template<typename Comp>
-    const_iterator_type cend() const noexcept {
-        return Pool<Comp>::cend();
-    }
-
-    template<typename Comp>
-    bool has(entity_type entity) const noexcept {
-        return Pool<Comp>::has(entity);
-    }
-
-    template<typename Comp>
-    const Comp & get(entity_type entity) const noexcept {
-        return Pool<Comp>::get(entity);
-    }
-
-    template<typename Comp>
-    Comp & get(entity_type entity) noexcept {
-        return const_cast<Comp &>(const_cast<const ComponentPool *>(this)->get<Comp>(entity));
-    }
-
-    template<typename Comp, typename... Args>
-    Comp & construct(entity_type entity, Args... args) {
-        return Pool<Comp>::construct(entity, args...);
-    }
-
-    template<typename Comp>
-    void destroy(entity_type entity) {
-        Pool<Comp>::destroy(entity);
-    }
-
-    template<typename Comp>
-    void reset() {
-        Pool<Comp>::reset();
-    }
-
-    void reset() {
-        using accumulator_type = int[];
-        Pool<Component>::reset();
-        accumulator_type accumulator = { (Pool<Components>::reset(), 0)... };
-        (void)accumulator;
-    }
-};
-
-
-}
-
-
-#endif // ENTT_COMPONENT_POOL_HPP

src/entt/core/family.hpp

@@ -0,0 +1,43 @@
+#ifndef ENTT_CORE_FAMILY_HPP
+#define ENTT_CORE_FAMILY_HPP
+
+
+#include<type_traits>
+#include<cstddef>
+#include<utility>
+
+
+namespace entt {
+
+
+/**
+ * @brief Dynamic identifier generator.
+ *
+ * Utility class template that can be used to assign unique identifiers to types
+ * at runtime. Use different specializations to create separate sets of
+ * identifiers.
+ */
+template<typename...>
+class Family {
+    static std::size_t identifier() noexcept {
+        static std::size_t value = 0;
+        return value++;
+    }
+
+public:
+    /**
+     * @brief Returns an unique identifier for the given type.
+     * @return Statically generated unique identifier for the given type.
+     */
+    template<typename...>
+    static std::size_t type() noexcept {
+        static const std::size_t value = identifier();
+        return value;
+    }
+};
+
+
+}
+
+
+#endif // ENTT_CORE_FAMILY_HPP

src/entt/core/ident.hpp

@@ -0,0 +1,71 @@
+#ifndef ENTT_CORE_IDENT_HPP
+#define ENTT_CORE_IDENT_HPP
+
+
+#include<type_traits>
+#include<cstddef>
+#include<utility>
+
+
+namespace entt {
+
+
+namespace {
+
+
+template<typename Type>
+struct Wrapper {
+    using type = Type;
+    constexpr Wrapper(std::size_t index): index{index} {}
+    const std::size_t index;
+};
+
+
+template<typename... Types>
+struct Identifier final: Wrapper<Types>... {
+    template<std::size_t... Indexes>
+    constexpr Identifier(std::index_sequence<Indexes...>): Wrapper<Types>{Indexes}... {}
+
+    template<typename Type>
+    constexpr std::size_t get() const { return Wrapper<std::decay_t<Type>>::index; }
+};
+
+
+}
+
+
+/**
+ * @brief Types identifers.
+ *
+ * Variable template used to generate identifiers at compile-time for the given
+ * types. Use the `constexpr` `get` member function to know what's the
+ * identifier associated to the specific type.
+ *
+ * @note
+ * Identifiers are constant expression and can be used in any context where such
+ * an expression is required. As an example:
+ * @code{.cpp}
+ * constexpr auto identifiers = entt::ident<AType, AnotherType>;
+ *
+ * switch(aTypeIdentifier) {
+ * case identifers.get<AType>():
+ *     // ...
+ *     break;
+ * case identifers.get<AnotherType>():
+ *     // ...
+ *     break;
+ * default:
+ *     // ...
+ * }
+ * @endcode
+ *
+ * @tparam Types The list of types for which to generate identifiers.
+ */
+template<typename... Types>
+constexpr auto ident = Identifier<std::decay_t<Types>...>{std::make_index_sequence<sizeof...(Types)>{}};
+
+
+}
+
+
+#endif // ENTT_CORE_IDENT_HPP

src/entt/entity/registry.hpp

@@ -0,0 +1,747 @@
+#ifndef ENTT_ENTITY_REGISTRY_HPP
+#define ENTT_ENTITY_REGISTRY_HPP
+
+
+#include <vector>
+#include <memory>
+#include <utility>
+#include <cstddef>
+#include <cassert>
+#include "../core/family.hpp"
+#include "sparse_set.hpp"
+#include "traits.hpp"
+#include "view.hpp"
+
+
+namespace entt {
+
+
+/**
+ * @brief A repository class for entities and components.
+ *
+ * The registry is the core class of the entity-component framework.<br/>
+ * It stores entities and arranges pools of components on a per request basis.
+ * By means of a registry, users can manage entities and components and thus
+ * create views to iterate them.
+ *
+ * @tparam Entity A valid entity type (see entt_traits for more details).
+ */
+template<typename Entity>
+class Registry {
+    using component_family = Family<struct InternalRegistryComponentFamily>;
+    using view_family = Family<struct InternalRegistryViewFamily>;
+    using traits_type = entt_traits<Entity>;
+
+    template<typename Component>
+    struct Pool: SparseSet<Entity, Component> {
+        using test_fn_type = bool(Registry::*)(Entity) const;
+
+        template<typename... Args>
+        Component & construct(Registry &registry, Entity entity, Args&&... args) {
+            auto &component = SparseSet<Entity, Component>::construct(entity, std::forward<Args>(args)...);
+
+            for(auto &&listener: listeners) {
+                if((registry.*listener.second)(entity)) {
+                    listener.first.construct(entity);
+                }
+            }
+
+            return component;
+        }
+
+        void destroy(Entity entity) override {
+            SparseSet<Entity, Component>::destroy(entity);
+
+            for(auto &&listener: listeners) {
+                auto &handler = listener.first;
+
+                if(handler.has(entity)) {
+                    handler.destroy(entity);
+                }
+            }
+        }
+
+        void append(SparseSet<Entity> &handler, test_fn_type fn) {
+            listeners.emplace_back(handler, fn);
+        }
+
+    private:
+        std::vector<std::pair<SparseSet<Entity> &, test_fn_type>> listeners;
+    };
+
+    template<typename Component>
+    bool managed() const noexcept {
+        const auto ctype = component_family::type<Component>();
+        return ctype < pools.size() && pools[ctype];
+    }
+
+    template<typename Component>
+    const Pool<Component> & pool() const noexcept {
+        assert(managed<Component>());
+        return static_cast<Pool<Component> &>(*pools[component_family::type<Component>()]);
+    }
+
+    template<typename Component>
+    Pool<Component> & pool() noexcept {
+        assert(managed<Component>());
+        return const_cast<Pool<Component> &>(const_cast<const Registry *>(this)->pool<Component>());
+    }
+
+    template<typename Component>
+    Pool<Component> & ensure() {
+        const auto ctype = component_family::type<Component>();
+
+        if(!(ctype < pools.size())) {
+            pools.resize(ctype + 1);
+        }
+
+        if(!pools[ctype]) {
+            pools[ctype] = std::make_unique<Pool<Component>>();
+        }
+
+        return pool<Component>();
+    }
+
+public:
+    /*! @brief Underlying entity identifier. */
+    using entity_type = typename traits_type::entity_type;
+    /*! @brief Underlying version type. */
+    using version_type = typename traits_type::version_type;
+    /*! @brief Unsigned integer type. */
+    using size_type = std::size_t;
+
+    /*! @brief Default constructor, explicit on purpose. */
+    explicit Registry() = default;
+    /*! @brief Default destructor. */
+    ~Registry() = default;
+
+    /*! @brief Copying a sparse set isn't allowed. */
+    Registry(const Registry &) = delete;
+    /*! @brief Moving a sparse set isn't allowed. */
+    Registry(Registry &&) = delete;
+
+    /*! @brief Copying a sparse set isn't allowed. @return This sparse set. */
+    Registry & operator=(const Registry &) = delete;
+    /*! @brief Moving a sparse set isn't allowed. @return This sparse set. */
+    Registry & operator=(Registry &&) = delete;
+
+    /**
+     * @brief Returns the number of existing components of the given type.
+     * @tparam Component The type of the component to which to return the size.
+     * @return The number of existing components of the given type.
+     */
+    template<typename Component>
+    size_type size() const noexcept {
+        return managed<Component>() ? pool<Component>().size() : size_type{};
+    }
+
+    /**
+     * @brief Returns the number of entities still in use.
+     * @return The number of entities still in use.
+     */
+    size_type size() const noexcept {
+        return entities.size() - available.size();
+    }
+
+    /**
+     * @brief Returns the number of entities ever created.
+     * @return The number of entities ever created.
+     */
+    size_type capacity() const noexcept {
+        return entities.size();
+    }
+
+    /**
+     * @brief Checks whether the pool for the given component is empty.
+     * @tparam Component The type of the component in which one is interested.
+     * @return True if the pool for the given component is empty, false
+     * otherwise.
+     */
+    template<typename Component>
+    bool empty() const noexcept {
+        return managed<Component>() ? pool<Component>().empty() : true;
+    }
+
+    /**
+     * @brief Checks if there exists at least an entity still in use.
+     * @return True if at least an entity is still in use, false otherwise.
+     */
+    bool empty() const noexcept {
+        return entities.size() == available.size();
+    }
+
+    /**
+     * @brief Verifies if the entity identifier still refers to a valid entity.
+     * @param entity An entity identifier, either valid or not.
+     * @return True if the identifier is still valid, false otherwise.
+     */
+    bool valid(entity_type entity) const noexcept {
+        const auto entt = entity & traits_type::entity_mask;
+        return (entt < entities.size() && entities[entt] == entity);
+    }
+
+    /**
+     * @brief Returns the version stored along with the given entity identifier.
+     * @param entity An entity identifier, either valid or not.
+     * @return The version stored along with the given entity identifier.
+     */
+    version_type version(entity_type entity) const noexcept {
+        return version_type((entity >> traits_type::version_shift) & traits_type::version_mask);
+    }
+
+    /**
+     * @brief Returns the actual version for the given entity identifier.
+     *
+     * In case entity identifers are stored around, this function can be used to
+     * know if they are still valid or the entity has been destroyed and
+     * potentially recycled.
+     *
+     * @warning
+     * Attempting to use an entity that doesn't belong to the registry results
+     * in undefined behavior. An entity belongs to the registry even if it has
+     * been previously destroyed and/or recycled.<br/>
+     * An assertion will abort the execution at runtime in debug mode if the
+     * registry doesn't own the given entity.
+     *
+     * @param entity A valid entity identifier.
+     * @return The actual version for the given entity identifier.
+     */
+    version_type current(entity_type entity) const noexcept {
+        const auto entt = entity & traits_type::entity_mask;
+        assert(entt < entities.size());
+        return version_type((entities[entt] >> traits_type::version_shift) & traits_type::version_mask);
+    }
+
+    /**
+     * @brief Returns a new entity to which the given components are assigned.
+     *
+     * There are two kinds of entity identifiers:
+     * * Newly created ones in case no entities have been previously destroyed.
+     * * Recycled one with updated versions.
+     *
+     * Users should not care about the type of the returned entity identifier.
+     * In case entity identifers are stored around, the `current` member
+     * function can be used to know if they are still valid or the entity has
+     * been destroyed and potentially recycled.
+     *
+     * @tparam Component A list of components to assign to the entity.
+     * @return A valid entity identifier.
+     */
+    template<typename... Component>
+    entity_type create() noexcept {
+        using accumulator_type = int[];
+        const auto entity = create();
+        accumulator_type accumulator = { 0, (ensure<Component>().construct(*this, entity), 0)... };
+        (void)accumulator;
+        return entity;
+    }
+
+    /**
+     * @brief Creates a new entity and returns it.
+     *
+     * There are two kinds of entity identifiers:
+     * * Newly created ones in case no entities have been previously destroyed.
+     * * Recycled one with updated versions.
+     *
+     * Users should not care about the type of the returned entity identifier.
+     * In case entity identifers are stored around, the `current` member
+     * function can be used to know if they are still valid or the entity has
+     * been destroyed and potentially recycled.
+     *
+     * @return A valid entity identifier.
+     */
+    entity_type create() noexcept {
+        entity_type entity;
+
+        if(available.empty()) {
+            entity = entity_type(entities.size());
+            assert((entity >> traits_type::version_shift) == entity_type{});
+            entities.push_back(entity);
+        } else {
+            entity = available.back();
+            available.pop_back();
+        }
+
+        return entity;
+    }
+
+    /**
+     * @brief Destroys an entity and lets the registry recycle the identifier.
+     *
+     * When an entity is destroyed, its version is updated and the identifier
+     * can be recycled at any time. In case entity identifers are stored around,
+     * the `current` member function can be used to know if they are still valid
+     * or the entity has been destroyed and potentially recycled.
+     *
+     * @warning
+     * Attempting to use an invalid entity results in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode in case of
+     * invalid entity.
+     *
+     * @param entity A valid entity identifier
+     */
+    void destroy(entity_type entity) {
+        assert(valid(entity));
+
+        const auto entt = entity & traits_type::entity_mask;
+        const auto version = 1 + ((entity >> traits_type::version_shift) & traits_type::version_mask);
+        const auto next = entt | (version << traits_type::version_shift);
+        entities[entt] = next;
+        available.push_back(next);
+
+        for(auto &&cpool: pools) {
+            if(cpool && cpool->has(entity)) {
+                cpool->destroy(entity);
+            }
+        }
+    }
+
+    /**
+     * @brief Assigns the given component to the given entity.
+     *
+     * A new instance of the given component is created and initialized with the
+     * arguments provided (the component must have a proper constructor or be of
+     * aggregate type). Then the component is assigned to the given entity.
+     *
+     * @warning
+     * Attempting to use an invalid entity or to assign a component to an entity
+     * that already owns it results in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode in case of
+     * invalid entity or if the entity already owns an instance of the given
+     * component.
+     *
+     * @tparam Component The type of the component to create.
+     * @tparam Args The types of the arguments used to construct the component.
+     * @param entity A valid entity identifier.
+     * @param args The parameters to use to initialize the component.
+     * @return A reference to the newly created component.
+     */
+    template<typename Component, typename... Args>
+    Component & assign(entity_type entity, Args&&... args) {
+        assert(valid(entity));
+        return ensure<Component>().construct(*this, entity, std::forward<Args>(args)...);
+    }
+
+    /**
+     * @brief Removes the given component from the given entity.
+     *
+     * @warning
+     * Attempting to use an invalid entity or to remove a component from an
+     * entity that doesn't own it results in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode in case of
+     * invalid entity or if the entity doesn't own an instance of the given
+     * component.
+     *
+     * @tparam Component The type of the component to remove.
+     * @param entity A valid entity identifier.
+     */
+    template<typename Component>
+    void remove(entity_type entity) {
+        assert(valid(entity));
+        return pool<Component>().destroy(entity);
+    }
+
+    /**
+     * @brief Checks if the given entity has all the given components.
+     *
+     * @warning
+     * Attempting to use an invalid entity results in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode in case of
+     * invalid entity.
+     *
+     * @tparam Component The components for which to perform the check.
+     * @param entity A valid entity identifier.
+     * @return True if the entity has all the components, false otherwise.
+     */
+    template<typename... Component>
+    bool has(entity_type entity) const noexcept {
+        static_assert(sizeof...(Component) > 0, "!");
+        assert(valid(entity));
+        using accumulator_type = bool[];
+        bool all = true;
+        accumulator_type accumulator = { (all = all && managed<Component>() && pool<Component>().has(entity))... };
+        (void)accumulator;
+        return all;
+    }
+
+    /**
+     * @brief Gets a reference to the given component owned by the given entity.
+     *
+     * @warning
+     * Attempting to use an invalid entity or to get a component from an entity
+     * that doesn't own it results in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode in case of
+     * invalid entity or if the entity doesn't own an instance of the given
+     * component.
+     *
+     * @tparam Component The type of the component to get.
+     * @param entity A valid entity identifier.
+     * @return A reference to the instance of the component owned by the entity.
+     */
+    template<typename Component>
+    const Component & get(entity_type entity) const noexcept {
+        assert(valid(entity));
+        return pool<Component>().get(entity);
+    }
+
+    /**
+     * @brief Gets a reference to the given component owned by the given entity.
+     *
+     * @warning
+     * Attempting to use an invalid entity or to get a component from an entity
+     * that doesn't own it results in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode in case of
+     * invalid entity or if the entity doesn't own an instance of the given
+     * component.
+     *
+     * @tparam Component The type of the component to get.
+     * @param entity A valid entity identifier.
+     * @return A reference to the instance of the component owned by the entity.
+     */
+    template<typename Component>
+    Component & get(entity_type entity) noexcept {
+        return const_cast<Component &>(const_cast<const Registry *>(this)->get<Component>(entity));
+    }
+
+    /**
+     * @brief Replaces the given component for the given entity.
+     *
+     * A new instance of the given component is created and initialized with the
+     * arguments provided (the component must have a proper constructor or be of
+     * aggregate type). Then the component is assigned to the given entity.
+     *
+     * @warning
+     * Attempting to use an invalid entity or to replace a component of an
+     * entity that doesn't own it results in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode in case of
+     * invalid entity or if the entity doesn't own an instance of the given
+     * component.
+     *
+     * @tparam Component The type of the component to replace.
+     * @tparam Args The types of the arguments used to construct the component.
+     * @param entity A valid entity identifier.
+     * @param args The parameters to use to initialize the component.
+     * @return A reference to the newly created component.
+     */
+    template<typename Component, typename... Args>
+    Component & replace(entity_type entity, Args&&... args) {
+        assert(valid(entity));
+        return (pool<Component>().get(entity) = Component{std::forward<Args>(args)...});
+    }
+
+    /**
+     * @brief Assigns or replaces the given component to the given entity.
+     *
+     * Equivalent to the following snippet (pseudocode):
+     *
+     * @code{.cpp}
+     * if(registry.has<Component>(entity)) {
+     *     registry.replace<Component>(entity, args...);
+     * } else {
+     *     registry.assign<Component>(entity, args...);
+     * }
+     * @endcode
+     *
+     * Prefer this function anyway because it has slighlty better
+     * performance.
+     *
+     * @warning
+     * Attempting to use an invalid entity results in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode in case of
+     * invalid entity.
+     *
+     * @tparam Component The type of the component to assign or replace.
+     * @tparam Args The types of the arguments used to construct the component.
+     * @param entity A valid entity identifier.
+     * @param args The parameters to use to initialize the component.
+     * @return A reference to the newly created component.
+     */
+    template<typename Component, typename... Args>
+    Component & accomodate(entity_type entity, Args&&... args) {
+        assert(valid(entity));
+        auto &cpool = ensure<Component>();
+
+        return (cpool.has(entity)
+                ? (cpool.get(entity) = Component{std::forward<Args>(args)...})
+                : cpool.construct(*this, entity, std::forward<Args>(args)...));
+    }
+
+    /**
+     * @brief Sorts the pool of the given component.
+     *
+     * The order of the elements in a pool is highly affected by assignements
+     * of components to entities and deletions. Components are arranged to
+     * maximize the performance during iterations and users should not make any
+     * assumption on the order.<br/>
+     * This function can be used to impose an order to the elements in the pool
+     * for the given component. The order is kept valid until a component of the
+     * given type is assigned or removed from an entity.
+     *
+     * The comparison function object must return `true` if the first element
+     * is _less_ than the second one, `false` otherwise. The signature of the
+     * comparison function should be equivalent to the following:
+     *
+     * @code{.cpp}
+     * bool(auto e1, auto e2)
+     * @endcode
+     *
+     * Where `e1` and `e2` are valid entity identifiers.
+     *
+     * @tparam Component The type of the components to sort.
+     * @tparam Compare The type of the comparison function object.
+     * @param compare A valid comparison function object.
+     */
+    template<typename Component, typename Compare>
+    void sort(Compare compare) {
+        auto &cpool = ensure<Component>();
+
+        cpool.sort([&cpool, compare = std::move(compare)](auto lhs, auto rhs) {
+            return compare(static_cast<const Component &>(cpool.get(lhs)), static_cast<const Component &>(cpool.get(rhs)));
+        });
+    }
+
+    /**
+     * @brief Sorts two pools of components in the same way.
+     *
+     * The order of the elements in a pool is highly affected by assignements
+     * of components to entities and deletions. Components are arranged to
+     * maximize the performance during iterations and users should not make any
+     * assumption on the order.
+     *
+     * It happens that different pools of components must be sorted the same way
+     * because of runtime and/or performance constraints. This function can be
+     * used to order a pool of components according to the order between the
+     * entities in another pool of components.
+     *
+     * @b How @b it @b works
+     *
+     * Being `A` and `B` the two sets where `B` is the master (the one the order
+     * of which rules) and `A` is the slave (the one to sort), after a call to
+     * this function an iterator for `A` will return the entities according to
+     * the following rules:
+     *
+     * * All the entities in `A` that are also in `B` are returned first
+     * according to the order they have in `B`.
+     * * All the entities in `A` that are not in `B` are returned in no
+     * particular order after all the other entities.
+     *
+     * Any subsequent change to `B` won't affect the order in `A`.
+     *
+     * @tparam To The type of the components to sort.
+     * @tparam From The type of the components to use to sort.
+     */
+    template<typename To, typename From>
+    void sort() {
+        ensure<To>().respect(ensure<From>());
+    }
+
+    /**
+     * @brief Resets the given component for the given entity.
+     *
+     * If the entity has an instance of the component, this function removes the
+     * component from the entity. Otherwise it does nothing.
+     *
+     * @warning
+     * Attempting to use an invalid entity results in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode in case of
+     * invalid entity.
+     *
+     * @tparam Component The component to reset.
+     * @param entity A valid entity identifier.
+     */
+    template<typename Component>
+    void reset(entity_type entity) {
+        assert(valid(entity));
+
+        if(managed<Component>()) {
+            auto &cpool = pool<Component>();
+
+            if(cpool.has(entity)) {
+                cpool.destroy(entity);
+            }
+        }
+    }
+
+    /**
+     * @brief Resets the pool of the given component.
+     *
+     * For each entity that has an instance of the given component, the
+     * component itself is removed and thus destroyed.
+     *
+     * @tparam Component The component whose pool must be reset.
+     */
+    template<typename Component>
+    void reset() {
+        if(managed<Component>()) {
+            auto &cpool = pool<Component>();
+
+            for(auto entity: entities) {
+                if(cpool.has(entity)) {
+                    cpool.destroy(entity);
+                }
+            }
+        }
+    }
+
+    /**
+     * @brief Resets the whole registry.
+     *
+     * Destroys all the entities. After a call to `reset`, all the entities
+     * previously created are recycled with a new version number. In case entity
+     * identifers are stored around, the `current` member function can be used
+     * to know if they are still valid.
+     */
+    void reset() {
+        available.clear();
+        pools.clear();
+
+        for(auto &&entity: entities) {
+            const auto version = 1 + ((entity >> traits_type::version_shift) & traits_type::version_mask);
+            entity = (entity & traits_type::entity_mask) | (version << traits_type::version_shift);
+            available.push_back(entity);
+        }
+    }
+
+    /**
+     * @brief Returns a standard view for the given components.
+     *
+     * This kind of views are created on the fly and share with the registry its
+     * internal data structures.<br/>
+     * Feel free to discard a view after the use. Creating and destroying a view
+     * is an incredibly cheap operation because they do not require any type of
+     * initialization.<br/>
+     * As a rule of thumb, storing a view should never be an option.
+     *
+     * Standard views do their best to iterate the smallest set of candidate
+     * entites. In particular:
+     * * Single component views are incredibly fast and iterate a packed array
+     * of entities, all of which has the given component.
+     * * Multi component views look at the number of entities available for each
+     * component and pick up a reference to the smallest set of candidates to
+     * test for the given components.
+     *
+     * @note
+     * Multi component views are pretty fast. However their performance tend to
+     * degenerate when the number of components to iterate grows up and the most
+     * of the entities have all the given components.<br/>
+     * To get a performance boost, consider using a PersistentView instead.
+     *
+     * @see View
+     * @see View<Entity, Component>
+     * @see PersistentView
+     *
+     * @tparam Component The type of the components used to construct the view.
+     * @return A newly created standard view.
+     */
+    template<typename... Component>
+    View<Entity, Component...> view() {
+        return View<Entity, Component...>{ensure<Component>()...};
+    }
+
+    /**
+     * @brief Prepares the internal data structures used by persistent views.
+     *
+     * Persistent views are an incredibly fast tool used to iterate a packed
+     * array of entities all of which have specific components.<br/>
+     * The initialization of a persistent view is also a pretty cheap operation,
+     * but for the first time they are created. That's mainly because of the
+     * internal data structures of the registry that are dedicated to this kind
+     * of views and that don't exist yet the very first time they are
+     * requested.<br/>
+     * To avoid costly operations, internal data structures for persistent views
+     * can be prepared with this function. Just use the same set of components
+     * that would have been used otherwise to contruct the view.
+     *
+     * @tparam Component The types of the components used to prepare the view.
+     */
+    template<typename... Component>
+    void prepare() {
+        static_assert(sizeof...(Component) > 1, "!");
+        const auto vtype = view_family::type<Component...>();
+
+        if(!(vtype < handlers.size())) {
+            handlers.resize(vtype + 1);
+        }
+
+        if(!handlers[vtype]) {
+            using accumulator_type = int[];
+
+            auto handler = std::make_unique<SparseSet<Entity>>();
+
+            for(auto entity: view<Component...>()) {
+                handler->construct(entity);
+            }
+
+            accumulator_type accumulator = {
+                (ensure<Component>().append(*handler, &Registry::has<Component...>), 0)...
+            };
+
+            handlers[vtype] = std::move(handler);
+            (void)accumulator;
+        }
+    }
+
+    /**
+     * @brief Returns a persistent view for the given components.
+     *
+     * This kind of views are created on the fly and share with the registry its
+     * internal data structures.<br/>
+     * Feel free to discard a view after the use. Creating and destroying a view
+     * is an incredibly cheap operation because they do not require any type of
+     * initialization.<br/>
+     * As a rule of thumb, storing a view should never be an option.
+     *
+     * Persistent views are the right choice to iterate entites when the number
+     * of components grows up and the most of the entities have all the given
+     * components.<br/>
+     * However they have also drawbacks:
+     * * Each kind of persistent view requires a dedicated data structure that
+     * is allocated within the registry and it increases memory pressure.
+     * * Internal data structures used to construct persistent views must be
+     * kept updated and it affects slightly construction and destruction of
+     * entities and components.
+     *
+     * That being said, persistent views are an incredibly powerful tool if used
+     * with care and offer a boost of performance undoubtedly.
+     *
+     * @note
+     * Consider to use the `prepare` member function to initialize the internal
+     * data structures used by persistent views when the registry is still
+     * empty. Initialization could be a costly operation otherwise and it will
+     * be performed the very first time each view is created.
+     *
+     * @see View
+     * @see View<Entity, Component>
+     * @see PersistentView
+     *
+     * @tparam Component The types of the components used to construct the view.
+     * @return A newly created persistent view.
+     */
+    template<typename... Component>
+    PersistentView<Entity, Component...> persistent() {
+        static_assert(sizeof...(Component) > 1, "!");
+        prepare<Component...>();
+        return PersistentView<Entity, Component...>{*handlers[view_family::type<Component...>()], ensure<Component>()...};
+    }
+
+private:
+    std::vector<std::unique_ptr<SparseSet<Entity>>> handlers;
+    std::vector<std::unique_ptr<SparseSet<Entity>>> pools;
+    std::vector<entity_type> available;
+    std::vector<entity_type> entities;
+};
+
+
+/**
+ * @brief Default registry class.
+ *
+ * The default registry is the best choice for almost all the applications.<br/>
+ * Users should have a really good reason to choose something different.
+ */
+using DefaultRegistry = Registry<std::uint32_t>;
+
+
+}
+
+
+#endif // ENTT_ENTITY_REGISTRY_HPP

src/entt/entity/sparse_set.hpp

@@ -0,0 +1,575 @@
+#ifndef ENTT_ENTITY_SPARSE_SET_HPP
+#define ENTT_ENTITY_SPARSE_SET_HPP
+
+
+#include <algorithm>
+#include <utility>
+#include <vector>
+#include <cstddef>
+#include <cassert>
+#include "traits.hpp"
+
+
+namespace entt {
+
+
+/**
+ * @brief Sparse set.
+ *
+ * Primary template isn't defined on purpose. All the specializations give a
+ * compile-time error, but for a few reasonable cases.
+ */
+template<typename...>
+class SparseSet;
+
+
+/**
+ * @brief Basic sparse set implementation.
+ *
+ * Sparse set or packed array or whatever is the name users give it.<br/>
+ * Two arrays: an _external_ one and an _internal_ one; a _sparse_ one and a
+ * _packed_ one; one used for direct access through contiguous memory, the other
+ * one used to get the data through an extra level of indirection.<br/>
+ * This is largely used by the Registry to offer users the fastest access ever
+ * to the components. View and PersistentView are entirely designed around
+ * sparse sets.
+ *
+ * This type of data structure is widely documented in the literature and on the
+ * web. This is nothing more than a customized implementation suitable for the
+ * purpose of the framework.
+ *
+ * @note
+ * There are no guarantees that entities are returned in the insertion order
+ * when iterate a sparse set. Do not make assumption on the order in any case.
+ *
+ * @note
+ * Internal data structures arrange elements to maximize performance. Because of
+ * that, there are no guarantees that elements have the expected order when
+ * iterate directly the internal packed array (see `data` and `size` member
+ * functions for that). Use `begin` and `end` instead.
+ *
+ * @tparam Entity A valid entity type (see entt_traits for more details).
+ */
+template<typename Entity>
+class SparseSet<Entity> {
+    using traits_type = entt_traits<Entity>;
+
+    struct Iterator {
+        using value_type = Entity;
+
+        Iterator(const std::vector<Entity> *direct, std::size_t pos)
+            : direct{direct}, pos{pos}
+        {}
+
+        Iterator & operator++() noexcept {
+            return --pos, *this;
+        }
+
+        Iterator operator++(int) noexcept {
+            Iterator orig = *this;
+            return ++(*this), orig;
+        }
+
+        bool operator==(const Iterator &other) const noexcept {
+            return other.pos == pos && other.direct == direct;
+        }
+
+        bool operator!=(const Iterator &other) const noexcept {
+            return !(*this == other);
+        }
+
+        value_type operator*() const noexcept {
+            return (*direct)[pos-1];
+        }
+
+    private:
+        const std::vector<Entity> *direct;
+        std::size_t pos;
+    };
+
+public:
+    /*! @brief Underlying entity identifier. */
+    using entity_type = Entity;
+    /*! @brief Entity dependent position type. */
+    using pos_type = entity_type;
+    /*! @brief Unsigned integer type. */
+    using size_type = std::size_t;
+    /*! @brief Input iterator type. */
+    using iterator_type = Iterator;
+
+    /*! @brief Default constructor, explicit on purpose. */
+    explicit SparseSet() noexcept = default;
+
+    /*! @brief Copying a sparse set isn't allowed. */
+    SparseSet(const SparseSet &) = delete;
+    /*! @brief Default move constructor. */
+    SparseSet(SparseSet &&) = default;
+
+    /*! @brief Default destructor. */
+    virtual ~SparseSet() noexcept = default;
+
+    /*! @brief Copying a sparse set isn't allowed. @return This sparse set. */
+    SparseSet & operator=(const SparseSet &) = delete;
+    /*! @brief Default move operator. @return This sparse set. */
+    SparseSet & operator=(SparseSet &&) = default;
+
+    /**
+     * @brief Returns the number of elements in the sparse set.
+     *
+     * The number of elements is also the size of the internal packed array.
+     * There is no guarantee that the internal sparse array has the same size.
+     * Usually the size of the internal sparse array is equal or greater than
+     * the one of the internal packed array.
+     *
+     * @return The number of elements.
+     */
+    size_type size() const noexcept {
+        return direct.size();
+    }
+
+    /**
+     * @brief Checks whether the sparse set is empty.
+     * @return True is the sparse set is empty, false otherwise.
+     */
+    bool empty() const noexcept {
+        return direct.empty();
+    }
+
+    /**
+     * @brief Direct access to the internal packed array.
+     *
+     * The returned pointer is such that range `[data(), data() + size()]` is
+     * always a valid range, even if the container is empty.
+     *
+     * @note
+     * There are no guarantees on the order, even though `sort` has been
+     * previously invoked. Internal data structures arrange elements to maximize
+     * performance. Accessing them directly gives a performance boost but less
+     * guarantees. Use `begin` and `end` if you want to iterate the sparse set
+     * in the expected order.
+     *
+     * @return A pointer to the internal packed array.
+     */
+    const entity_type * data() const noexcept {
+        return direct.data();
+    }
+
+    /**
+     * @brief Returns an iterator to the beginning.
+     *
+     * The returned iterator points to the first element of the internal packed
+     * array. If the sparse set is empty, the returned iterator will be equal to
+     * `end()`.
+     *
+     * @note
+     * Input iterators stay true to the order imposed by a call to `sort`.
+     *
+     * @return An iterator to the first element of the internal packed array.
+     */
+    iterator_type begin() const noexcept {
+        return Iterator{&direct, direct.size()};
+    }
+
+    /**
+     * @brief Returns an iterator to the end.
+     *
+     * The returned iterator points to the element following the last element in
+     * the internal packed array. Attempting to dereference the returned
+     * iterator results in undefined behavior.
+     *
+     * @note
+     * Input iterators stay true to the order imposed by a call to `sort`.
+     *
+     * @return An iterator to the element following the last element of the
+     * internal packed array.
+     */
+    iterator_type end() const noexcept {
+        return Iterator{&direct, 0};
+    }
+
+    /**
+     * @brief Checks if the sparse set contains the given entity.
+     * @param entity A valid entity identifier.
+     * @return True if the sparse set contains the entity, false otherwise.
+     */
+    bool has(entity_type entity) const noexcept {
+        const auto entt = entity & traits_type::entity_mask;
+        return entt < reverse.size() && reverse[entt] < direct.size() && direct[reverse[entt]] == entity;
+    }
+
+    /**
+     * @brief Returns the position of the entity in the sparse set.
+     *
+     * @warning
+     * Attempting to get the position of an entity that doesn't belong to the
+     * sparse set results in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode if the
+     * sparse set doesn't contain the given entity.
+     *
+     * @param entity A valid entity identifier.
+     * @return The position of the entity in the sparse set.
+     */
+    pos_type get(entity_type entity) const noexcept {
+        assert(has(entity));
+        return reverse[entity & traits_type::entity_mask];
+    }
+
+    /**
+     * @brief Assigns an entity to the sparse set.
+     *
+     * @warning
+     * Attempting to assign an entity that already belongs to the sparse set
+     * results in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode if the
+     * sparse set already contains the given entity.
+     *
+     * @param entity A valid entity identifier.
+     * @return The position of the entity in the internal packed array.
+     */
+    pos_type construct(entity_type entity) {
+        assert(!has(entity));
+        const auto entt = entity & traits_type::entity_mask;
+
+        if(!(entt < reverse.size())) {
+            reverse.resize(entt+1);
+        }
+
+        const auto pos = pos_type(direct.size());
+        reverse[entt] = pos;
+        direct.emplace_back(entity);
+
+        return pos;
+    }
+
+    /**
+     * @brief Removes the given entity from the sparse set.
+     *
+     * @warning
+     * Attempting to remove an entity that doesn't belong to the sparse set
+     * results in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode if the
+     * sparse set doesn't contain the given entity.
+     *
+     * @param entity A valid entity identifier.
+     */
+    virtual void destroy(entity_type entity) {
+        assert(has(entity));
+        const auto entt = entity & traits_type::entity_mask;
+        const auto back = direct.back() & traits_type::entity_mask;
+        const auto pos = reverse[entt];
+        reverse[back] = pos;
+        direct[pos] = direct.back();
+        direct.pop_back();
+    }
+
+    /**
+     * @brief Swaps the position of the entities in the internal packed array.
+     *
+     * For what it's worth, this function affects both the internal sparse array
+     * and the internal packed array. Users should not care of that anyway.
+     *
+     * @warning
+     * Attempting to swap entities that don't belong to the sparse set results
+     * in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode if the
+     * sparse set doesn't contain the given entities.
+     *
+     * @param lhs A valid entity identifier.
+     * @param rhs A valid entity identifier.
+     */
+    virtual void swap(entity_type lhs, entity_type rhs) {
+        assert(has(lhs));
+        assert(has(rhs));
+        const auto le = lhs & traits_type::entity_mask;
+        const auto re = rhs & traits_type::entity_mask;
+        std::swap(direct[reverse[le]], direct[reverse[re]]);
+        std::swap(reverse[le], reverse[re]);
+    }
+
+    /**
+     * @brief Sort entities according to the given comparison function.
+     *
+     * Sort the elements so that iterating the sparse set with a couple of
+     * iterators returns them in the expected order. See `begin` and `end` for
+     * more details.
+     *
+     * @note
+     * Attempting to iterate elements using the raw pointer returned by `data`
+     * gives no guarantees on the order, even though `sort` has been invoked.
+     *
+     * @tparam Compare The type of the comparison function.
+     * @param compare A comparison function whose signature shall be equivalent
+     * to: `bool(Entity, Entity)`.
+     */
+    template<typename Compare>
+    void sort(Compare compare) {
+        std::vector<pos_type> copy{direct.cbegin(), direct.cend()};
+        std::sort(copy.begin(), copy.end(), [compare = std::move(compare)](auto... args) {
+            return !compare(args...);
+        });
+
+        for(pos_type i = 0; i < copy.size(); ++i) {
+            if(direct[i] != copy[i]) {
+                swap(direct[i], copy[i]);
+            }
+        }
+    }
+
+    /**
+     * @brief Sort entities according to their order in the given sparse set.
+     *
+     * Entities that are part of both the sparse sets are ordered internally
+     * according to the order they have in `other`. All the other entities goes
+     * to the end of the list and there are no guarantess on their order.<br/>
+     * In other terms, this function can be used to impose the same order on two
+     * sets by using one of them as a master and the other one as a slave.
+     *
+     * Iterating the sparse set with a couple of iterators returns elements in
+     * the expected order after a call to `sort`. See `begin` and `end` for more
+     * details.
+     *
+     * @note
+     * Attempting to iterate elements using the raw pointer returned by `data`
+     * gives no guarantees on the order, even though `sort` has been invoked.
+     *
+     * @param other The sparse sets that imposes the order of the entities.
+     */
+    void respect(const SparseSet<Entity> &other) {
+        struct Bool { bool value{false}; };
+        std::vector<Bool> check(std::max(other.reverse.size(), reverse.size()));
+
+        for(auto entity: other.direct) {
+            check[entity & traits_type::entity_mask].value = true;
+        }
+
+        sort([this, &other, &check](auto lhs, auto rhs) {
+            const auto le = lhs & traits_type::entity_mask;
+            const auto re = rhs & traits_type::entity_mask;
+
+            const bool bLhs = check[le].value;
+            const bool bRhs = check[re].value;
+            bool compare = false;
+
+            if(bLhs && bRhs) {
+                compare = other.get(rhs) < other.get(lhs);
+            } else if(!bLhs && !bRhs) {
+                compare = re < le;
+            } else {
+                compare = bLhs;
+            }
+
+            return compare;
+        });
+    }
+
+    /**
+     * @brief Resets the sparse set.
+     */
+    virtual void reset() {
+        reverse.clear();
+        direct.clear();
+    }
+
+private:
+    std::vector<entity_type> reverse;
+    std::vector<entity_type> direct;
+};
+
+
+/**
+ * @brief Extended sparse set implementation.
+ *
+ * This specialization of a sparse set associates an object to an entity. The
+ * main purpose of this class is to use sparse sets to store components in a
+ * Registry. It guarantees fast access both to the elements and to the entities.
+ *
+ * @note
+ * Entities and objects have the same order. It's guaranteed both in case of raw
+ * access (either to entities or objects) and when using input iterators.
+ *
+ * @note
+ * Internal data structures arrange elements to maximize performance. Because of
+ * that, there are no guarantees that elements have the expected order when
+ * iterate directly the internal packed array (see `raw` and `size` member
+ * functions for that). Use `begin` and `end` instead.
+ *
+ * @sa SparseSet<Entity>
+ *
+ * @tparam Entity A valid entity type (see entt_traits for more details).
+ * @tparam Type The type of the objects assigned to the entities.
+ */
+template<typename Entity, typename Type>
+class SparseSet<Entity, Type>: public SparseSet<Entity> {
+    using underlying_type = SparseSet<Entity>;
+
+public:
+    /*! @brief Type of the objects associated to the entities. */
+    using type = Type;
+    /*! @brief Underlying entity identifier. */
+    using entity_type = typename underlying_type::entity_type;
+    /*! @brief Entity dependent position type. */
+    using pos_type = typename underlying_type::pos_type;
+    /*! @brief Unsigned integer type. */
+    using size_type = typename underlying_type::size_type;
+    /*! @brief Input iterator type. */
+    using iterator_type = typename underlying_type::iterator_type;
+
+    /*! @brief Default constructor, explicit on purpose. */
+    explicit SparseSet() noexcept = default;
+
+    /*! @brief Copying a sparse set isn't allowed. */
+    SparseSet(const SparseSet &) = delete;
+    /*! @brief Default move constructor. */
+    SparseSet(SparseSet &&) = default;
+
+    /*! @brief Copying a sparse set isn't allowed. @return This sparse set. */
+    SparseSet & operator=(const SparseSet &) = delete;
+    /*! @brief Default move operator. @return This sparse set. */
+    SparseSet & operator=(SparseSet &&) = default;
+
+    /**
+     * @brief Direct access to the array of objects.
+     *
+     * The returned pointer is such that range `[raw(), raw() + size()]` is
+     * always a valid range, even if the container is empty.
+     *
+     * @note
+     * There are no guarantees on the order, even though `sort` has been
+     * previously invoked. Internal data structures arrange elements to maximize
+     * performance. Accessing them directly gives a performance boost but less
+     * guarantees. Use `begin` and `end` if you want to iterate the sparse set
+     * in the expected order.
+     *
+     * @return A pointer to the array of objects.
+     */
+    const type * raw() const noexcept {
+        return instances.data();
+    }
+
+    /**
+     * @brief Direct access to the array of objects.
+     *
+     * The returned pointer is such that range `[raw(), raw() + size()]` is
+     * always a valid range, even if the container is empty.
+     *
+     * @note
+     * There are no guarantees on the order, even though `sort` has been
+     * previously invoked. Internal data structures arrange elements to maximize
+     * performance. Accessing them directly gives a performance boost but less
+     * guarantees. Use `begin` and `end` if you want to iterate the sparse set
+     * in the expected order.
+     *
+     * @return A pointer to the array of objects.
+     */
+    type * raw() noexcept {
+        return instances.data();
+    }
+
+    /**
+     * @brief Returns the object associated to the given entity.
+     *
+     * @warning
+     * Attempting to use an entity that doesn't belong to the sparse set results
+     * in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode if the
+     * sparse set doesn't contain the given entity.
+     *
+     * @param entity A valid entity identifier.
+     * @return The object associated to the entity.
+     */
+    const type & get(entity_type entity) const noexcept {
+        return instances[underlying_type::get(entity)];
+    }
+
+    /**
+     * @brief Returns the object associated to the given entity.
+     *
+     * @warning
+     * Attempting to use an entity that doesn't belong to the sparse set results
+     * in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode if the
+     * sparse set doesn't contain the given entity.
+     *
+     * @param entity A valid entity identifier.
+     * @return The object associated to the entity.
+     */
+    type & get(entity_type entity) noexcept {
+        return const_cast<type &>(const_cast<const SparseSet *>(this)->get(entity));
+    }
+
+    /**
+     * @brief Assigns an entity to the sparse set and constructs its object.
+     *
+     * @warning
+     * Attempting to use an entity that already belongs to the sparse set
+     * results in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode if the
+     * sparse set already contains the given entity.
+     *
+     * @tparam Args The type of the params used to construct the object.
+     * @param entity A valid entity identifier.
+     * @param args The params to use to construct an object for the entity.
+     * @return The object associated to the entity.
+     */
+    template<typename... Args>
+    type & construct(entity_type entity, Args&&... args) {
+        underlying_type::construct(entity);
+        instances.push_back({ std::forward<Args>(args)... });
+        return instances.back();
+    }
+
+    /**
+     * @brief Removes an entity from the sparse set and destroies its object.
+     *
+     * @warning
+     * Attempting to use an entity that doesn't belong to the sparse set results
+     * in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode if the
+     * sparse set doesn't contain the given entity.
+     *
+     * @param entity A valid entity identifier.
+     */
+    void destroy(entity_type entity) override {
+        instances[underlying_type::get(entity)] = std::move(instances.back());
+        instances.pop_back();
+        underlying_type::destroy(entity);
+    }
+
+    /**
+     * @brief Swaps the two entities and their objects.
+     *
+     * @note
+     * This function doesn't swap objects between entities. It exchanges entity
+     * and object positions in the sparse set. It's used mainly for sorting.
+     *
+     * @warning
+     * Attempting to use entities that don't belong to the sparse set results
+     * in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode if the
+     * sparse set doesn't contain the given entities.
+     *
+     * @param lhs A valid entity identifier.
+     * @param rhs A valid entity identifier.
+     */
+    void swap(entity_type lhs, entity_type rhs) override {
+        std::swap(instances[underlying_type::get(lhs)], instances[underlying_type::get(rhs)]);
+        underlying_type::swap(lhs, rhs);
+    }
+
+    /**
+     * @brief Resets the sparse set.
+     */
+    void reset() override {
+        underlying_type::reset();
+        instances.clear();
+    }
+
+private:
+    std::vector<type> instances;
+};
+
+
+}
+
+
+#endif // ENTT_ENTITY_SPARSE_SET_HPP

src/entt/entity/traits.hpp

@@ -0,0 +1,93 @@
+#ifndef ENTT_ENTITY_ENTT_HPP
+#define ENTT_ENTITY_ENTT_HPP
+
+
+#include <cstdint>
+
+
+namespace entt {
+
+
+/**
+ * @brief Entity traits.
+ *
+ * Primary template isn't defined on purpose. All the specializations give a
+ * compile-time error unless the template parameter is an accepted entity type.
+ */
+template<typename>
+struct entt_traits;
+
+
+/**
+ * @brief Entity traits for a 16 bits entity identifier.
+ *
+ * A 16 bits entity identifier guarantees:
+ * * 12 bits for the entity number (up to 4k entities).
+ * * 4 bit for the version (resets in [0-15]).
+ */
+template<>
+struct entt_traits<std::uint16_t> {
+    /*! @brief Underlying entity type. */
+    using entity_type = std::uint16_t;
+    /*! @brief Underlying version type. */
+    using version_type = std::uint8_t;
+
+    /*! @brief Mask to use to get the entity number out of an identifier. */
+    static constexpr auto entity_mask = 0xFFF;
+    /*! @brief Mask to use to get the version out of an identifier. */
+    static constexpr auto version_mask = 0xF;
+    /*! @brief Extent of the entity number within an identifier. */
+    static constexpr auto version_shift = 12;
+};
+
+
+/**
+ * @brief Entity traits for a 32 bits entity identifier.
+ *
+ * A 32 bits entity identifier guarantees:
+ * * 24 bits for the entity number (suitable for almost all the games).
+ * * 8 bit for the version (resets in [0-255]).
+ */
+template<>
+struct entt_traits<std::uint32_t> {
+    /*! @brief Underlying entity type. */
+    using entity_type = std::uint32_t;
+    /*! @brief Underlying version type. */
+    using version_type = std::uint16_t;
+
+    /*! @brief Mask to use to get the entity number out of an identifier. */
+    static constexpr auto entity_mask = 0xFFFFFF;
+    /*! @brief Mask to use to get the version out of an identifier. */
+    static constexpr auto version_mask = 0xFF;
+    /*! @brief Extent of the entity number within an identifier. */
+    static constexpr auto version_shift = 24;
+};
+
+
+/**
+ * @brief Entity traits for a 64 bits entity identifier.
+ *
+ * A 64 bits entity identifier guarantees:
+ * * 40 bits for the entity number (an indecently large number).
+ * * 24 bit for the version (an indecently large number).
+ */
+template<>
+struct entt_traits<std::uint64_t> {
+    /*! @brief Underlying entity type. */
+    using entity_type = std::uint64_t;
+    /*! @brief Underlying version type. */
+    using version_type = std::uint32_t;
+
+    /*! @brief Mask to use to get the entity number out of an identifier. */
+    static constexpr auto entity_mask = 0xFFFFFFFFFF;
+    /*! @brief Mask to use to get the version out of an identifier. */
+    static constexpr auto version_mask = 0xFFFFFF;
+    /*! @brief Extent of the entity number within an identifier. */
+    static constexpr auto version_shift = 40;
+};
+
+
+}
+
+
+#endif // ENTT_ENTITY_ENTT_HPP

src/entt/entity/view.hpp

@@ -0,0 +1,633 @@
+#ifndef ENTT_ENTITY_VIEW_HPP
+#define ENTT_ENTITY_VIEW_HPP
+
+
+#include <tuple>
+#include "sparse_set.hpp"
+
+
+namespace entt {
+
+
+/**
+ * @brief Persistent view.
+ *
+ * A persistent view returns all the entities and only the entities that have
+ * at least the given components. Moreover, it's guaranteed that the entity list
+ * is thightly packed in memory for fast iterations.<br/>
+ * In general, persistent views don't stay true to the order of any set of
+ * components unless users explicitly sort them.
+ *
+ * @b Important
+ *
+ * Iterators aren't invalidated if:
+ *
+ * * New instances of the given components are created and assigned to entities.
+ * * The entity currently pointed is modified (as an example, if one of the
+ * given components is removed from the entity to which the iterator points).
+ *
+ * In all the other cases, modify the pools of the given components somehow
+ * invalidates all the iterators and using them results in undefined behavior.
+ *
+ * @note
+ * Views share references to the underlying data structures with the Registry
+ * that generated them. Therefore any change to the entities and to the
+ * components made by means of the registry are immediately reflected by
+ * views.<br/>
+ * Moreover, sorting a persistent view affects all the other views of the same
+ * type (it means that users don't have to call `sort` on each view to sort all
+ * of them because they share the set of entities).
+ *
+ * @warning
+ * Lifetime of a view must overcome the one of the registry that generated it.
+ * In any other case, attempting to use a view results in undefined behavior.
+ *
+ * @sa View
+ * @sa View<Entity, Component>
+ *
+ * @tparam Entity A valid entity type (see entt_traits for more details).
+ * @tparam Component The types of the components iterated by the view.
+ */
+template<typename Entity, typename... Component>
+class PersistentView final {
+    static_assert(sizeof...(Component) > 1, "!");
+
+    template<typename Comp>
+    using pool_type = SparseSet<Entity, Comp>;
+
+    using view_type = SparseSet<Entity>;
+
+public:
+    /*! Input iterator type. */
+    using iterator_type = typename view_type::iterator_type;
+    /*! @brief Underlying entity identifier. */
+    using entity_type = typename view_type::entity_type;
+    /*! @brief Unsigned integer type. */
+    using size_type = typename view_type::size_type;
+
+    /**
+     * @brief Constructs a persistent view around a dedicated pool of entities.
+     *
+     * A persistent view is created out of:
+     * * A dedicated pool of entities that is shared between all the persistent
+     * views of the same type.
+     * * A bunch of pools of components to which to refer to get instances.
+     *
+     * @param view Shared reference to a dedicated pool of entities.
+     * @param pools References to pools of components.
+     */
+    explicit PersistentView(view_type &view, pool_type<Component>&... pools) noexcept
+        : view{view}, pools{pools...}
+    {}
+
+    /**
+     * @brief Returns the number of entities that have the given components.
+     * @return The number of entities that have the given components.
+     */
+    size_type size() const noexcept {
+        return view.size();
+    }
+
+    /**
+     * @brief Direct access to the list of entities.
+     *
+     * The returned pointer is such that range `[data(), data() + size()]` is
+     * always a valid range, even if the container is empty.
+     *
+     * @note
+     * There are no guarantees on the order of the entities. Use `begin` and
+     * `end` if you want to iterate the view in the expected order.
+     *
+     * @return A pointer to the array of entities.
+     */
+    const entity_type * data() const noexcept {
+        return view.data();
+    }
+
+    /**
+     * @brief Returns an iterator to the first entity that has the given
+     * components.
+     *
+     * The returned iterator points to the first entity that has the given
+     * components. If the view is empty, the returned iterator will be equal to
+     * `end()`.
+     *
+     * @note
+     * Input iterators stay true to the order imposed to the underlying data
+     * structures.
+     *
+     * @return An iterator to the first entity that has the given components.
+     */
+    iterator_type begin() const noexcept {
+        return view.begin();
+    }
+
+    /**
+     * @brief Returns an iterator that is past the last entity that has the
+     * given components.
+     *
+     * The returned iterator points to the entity following the last entity that
+     * has the given components. Attempting to dereference the returned iterator
+     * results in undefined behavior.
+     *
+     * @note
+     * Input iterators stay true to the order imposed to the underlying data
+     * structures.
+     *
+     * @return An iterator to the entity following the last entity that has the
+     * given components.
+     */
+    iterator_type end() const noexcept {
+        return view.end();
+    }
+
+    /**
+     * @brief Returns the component assigned to the given entity.
+     *
+     * Prefer this function instead of `Registry::get` during iterations. It has
+     * far better performance than its companion function.
+     *
+     * @warning
+     * Attempting to use an invalid component type results in a compilation
+     * error. Attempting to use an entity that doesn't belong to the view
+     * results in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode if
+     * the view doesn't contain the given entity.
+     *
+     * @tparam Comp The type of the component to get.
+     * @param entity A valid entity identifier.
+     * @return The component assigned to the entity.
+     */
+    template<typename Comp>
+    const Comp & get(entity_type entity) const noexcept {
+        return std::get<pool_type<Comp> &>(pools).get(entity);
+    }
+
+    /**
+     * @brief Returns the component assigned to the given entity.
+     *
+     * Prefer this function instead of `Registry::get` during iterations.
+     * It has far better performance than its companion function.
+     *
+     * @warning
+     * Attempting to use an invalid component type results in a compilation
+     * error. Attempting to use an entity that doesn't belong to the view
+     * results in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode if
+     * the view doesn't contain the given entity.
+     *
+     * @tparam Comp The type of the component to get.
+     * @param entity A valid entity identifier.
+     * @return The component assigned to the entity.
+     */
+    template<typename Comp>
+    Comp & get(entity_type entity) noexcept {
+        return const_cast<Comp &>(const_cast<const PersistentView *>(this)->get<Comp>(entity));
+    }
+
+    /**
+     * @brief Sort the shared pool of entities according to the given component.
+     *
+     * Persistent views of the same type share with the Registry a pool of
+     * entities with its own order that doesn't depend on the order of any pool
+     * of components. Users can order the underlying data structure so that it
+     * respects the order of the pool of the given component.
+     *
+     * @note
+     * The shared pool of entities and thus its order is affected by the changes
+     * to each and every pool of components that it tracks. Therefore changes to
+     * the pools of components can quickly ruin the order imposed to the pool of
+     * entities shared between the persistent views.
+     *
+     * @tparam Comp The type of the component to use to impose the order.
+     */
+    template<typename Comp>
+    void sort() {
+        view.respect(std::get<pool_type<Comp> &>(pools));
+    }
+
+private:
+    view_type &view;
+    std::tuple<pool_type<Component> &...> pools;
+};
+
+
+/**
+ * @brief Multi component view.
+ *
+ * Multi component views iterate over those entities that have at least all the
+ * given components in their bags. During initialization, a multi component view
+ * looks at the number of entities available for each component and picks up a
+ * reference to the smallest set of candidate entities in order to get a
+ * performance boost when iterate.<br/>
+ * Order of elements during iterations are highly dependent on the order of the
+ * underlying data strctures. See SparseSet and its specializations for more
+ * details.
+ *
+ * @b Important
+ *
+ * Iterators aren't invalidated if:
+ *
+ * * New instances of the given components are created and assigned to entities.
+ * * The entity currently pointed is modified (as an example, if one of the
+ * given components is removed from the entity to which the iterator points).
+ *
+ * In all the other cases, modify the pools of the given components somehow
+ * invalidates all the iterators and using them results in undefined behavior.
+ *
+ * @note
+ * Views share references to the underlying data structures with the Registry
+ * that generated them. Therefore any change to the entities and to the
+ * components made by means of the registry are immediately reflected by views.
+ *
+ * @warning
+ * Lifetime of a view must overcome the one of the registry that generated it.
+ * In any other case, attempting to use a view results in undefined behavior.
+ *
+ * @sa View<Entity, Component>
+ * @sa PersistentView
+ *
+ * @tparam Entity A valid entity type (see entt_traits for more details).
+ * @tparam First One of the components to iterate.
+ * @tparam Other The rest of the components to iterate.
+ */
+template<typename Entity, typename First, typename... Other>
+class View final {
+    template<typename Component>
+    using pool_type = SparseSet<Entity, Component>;
+
+    using base_pool_type = SparseSet<Entity>;
+    using underlying_iterator_type = typename base_pool_type::iterator_type;
+    using repo_type = std::tuple<pool_type<First> &, pool_type<Other> &...>;
+
+    class Iterator {
+        inline bool valid() const noexcept {
+            using accumulator_type = bool[];
+            auto entity = *begin;
+            bool all = std::get<pool_type<First> &>(pools).has(entity);
+            accumulator_type accumulator =  { (all = all && std::get<pool_type<Other> &>(pools).has(entity))... };
+            (void)accumulator;
+            return all;
+        }
+
+    public:
+        using value_type = typename base_pool_type::entity_type;
+
+        Iterator(const repo_type &pools, underlying_iterator_type begin, underlying_iterator_type end) noexcept
+            : pools{pools}, begin{begin}, end{end}
+        {
+            if(begin != end && !valid()) {
+                ++(*this);
+            }
+        }
+
+        Iterator & operator++() noexcept {
+            ++begin;
+            while(begin != end && !valid()) { ++begin; }
+            return *this;
+        }
+
+        Iterator operator++(int) noexcept {
+            Iterator orig = *this;
+            return ++(*this), orig;
+        }
+
+        bool operator==(const Iterator &other) const noexcept {
+            return other.begin == begin;
+        }
+
+        bool operator!=(const Iterator &other) const noexcept {
+            return !(*this == other);
+        }
+
+        value_type operator*() const noexcept {
+            return *begin;
+        }
+
+    private:
+        const repo_type &pools;
+        underlying_iterator_type begin;
+        underlying_iterator_type end;
+    };
+
+public:
+    /*! Input iterator type. */
+    using iterator_type = Iterator;
+    /*! @brief Underlying entity identifier. */
+    using entity_type = typename base_pool_type::entity_type;
+    /*! @brief Unsigned integer type. */
+    using size_type = typename base_pool_type::size_type;
+
+    /**
+     * @brief Constructs a view out of a bunch of pools of components.
+     * @param pool A reference to a pool of components.
+     * @param other Other references to pools of components.
+     */
+    explicit View(pool_type<First> &pool, pool_type<Other>&... other) noexcept
+        : pools{pool, other...}, view{nullptr}
+    {
+        reset();
+    }
+
+    /**
+     * @brief Returns an iterator to the first entity that has the given
+     * components.
+     *
+     * The returned iterator points to the first entity that has the given
+     * components. If the view is empty, the returned iterator will be equal to
+     * `end()`.
+     *
+     * @note
+     * Input iterators stay true to the order imposed to the underlying data
+     * structures.
+     *
+     * @return An iterator to the first entity that has the given components.
+     */
+    iterator_type begin() const noexcept {
+        return Iterator{pools, view->begin(), view->end()};
+    }
+
+    /**
+     * @brief Returns an iterator that is past the last entity that has the
+     * given components.
+     *
+     * The returned iterator points to the entity following the last entity that
+     * has the given components. Attempting to dereference the returned iterator
+     * results in undefined behavior.
+     *
+     * @note
+     * Input iterators stay true to the order imposed to the underlying data
+     * structures.
+     *
+     * @return An iterator to the entity following the last entity that has the
+     * given components.
+     */
+    iterator_type end() const noexcept {
+        return Iterator{pools, view->end(), view->end()};
+    }
+
+    /**
+     * @brief Returns the component assigned to the given entity.
+     *
+     * Prefer this function instead of `Registry::get` during iterations.
+     * It has far better performance than its companion function.
+     *
+     * @warning
+     * Attempting to use an invalid component type results in a compilation
+     * error. Attempting to use an entity that doesn't belong to the view
+     * results in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode if
+     * the view doesn't contain the given entity.
+     *
+     * @tparam Component The type of the component to get.
+     * @param entity A valid entity identifier.
+     * @return The component assigned to the entity.
+     */
+    template<typename Component>
+    const Component & get(entity_type entity) const noexcept {
+        return std::get<pool_type<Component> &>(pools).get(entity);
+    }
+
+    /**
+     * @brief Returns the component assigned to the given entity.
+     *
+     * Prefer this function instead of `Registry::get` during iterations. It has
+     * far better performance than its companion function.
+     *
+     * @warning
+     * Attempting to use an invalid component type results in a compilation
+     * error. Attempting to use an entity that doesn't belong to the view
+     * results in undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode if
+     * the view doesn't contain the given entity.
+     *
+     * @tparam Component The type of the component to get.
+     * @param entity A valid entity identifier.
+     * @return The component assigned to the entity.
+     */
+    template<typename Component>
+    Component & get(entity_type entity) noexcept {
+        return const_cast<Component &>(const_cast<const View *>(this)->get<Component>(entity));
+    }
+
+    /**
+     * @brief Resets the view and reinitializes it.
+     *
+     * A multi component view keeps a reference to the smallest set of candidate
+     * entities to iterate. Resetting a view means querying the underlying data
+     * structures and reinitializing the view.<br/>
+     * Use it only if copies of views are stored around and there is a
+     * possibility that a component has become the best candidate in the
+     * meantime.
+     */
+    void reset() {
+        using accumulator_type = void *[];
+        view = &std::get<pool_type<First> &>(pools);
+        accumulator_type accumulator = { (std::get<pool_type<Other> &>(pools).size() < view->size() ? (view = &std::get<pool_type<Other> &>(pools)) : nullptr)... };
+        (void)accumulator;
+    }
+
+private:
+    repo_type pools;
+    base_pool_type *view;
+};
+
+
+/**
+ * @brief Single component view specialization.
+ *
+ * Single component views are specialized in order to get a boost in terms of
+ * performance. This kind of views can access the underlying data structure
+ * directly and avoid superflous checks.<br/>
+ * Order of elements during iterations are highly dependent on the order of the
+ * underlying data structure. See SparseSet and its specializations for more
+ * details.
+ *
+ * @b Important
+ *
+ * Iterators aren't invalidated if:
+ *
+ * * New instances of the given components are created and assigned to entities.
+ * * The entity currently pointed is modified (as an example, if one of the
+ * given components is removed from the entity to which the iterator points).
+ *
+ * In all the other cases, modify the pools of the given components somehow
+ * invalidates all the iterators and using them results in undefined behavior.
+ *
+ * @note
+ * Views share a reference to the underlying data structure with the Registry
+ * that generated them. Therefore any change to the entities and to the
+ * components made by means of the registry are immediately reflected by views.
+ *
+ * @warning
+ * Lifetime of a view must overcome the one of the registry that generated it.
+ * In any other case, attempting to use a view results in undefined behavior.
+ *
+ * @sa View
+ * @sa PersistentView
+ *
+ * @tparam Entity A valid entity type (see entt_traits for more details).
+ * @tparam Component The type of the component iterated by the view.
+ */
+template<typename Entity, typename Component>
+class View<Entity, Component> final {
+    using pool_type = SparseSet<Entity, Component>;
+
+public:
+    /*! Input iterator type. */
+    using iterator_type = typename pool_type::iterator_type;
+    /*! @brief Underlying entity identifier. */
+    using entity_type = typename pool_type::entity_type;
+    /*! @brief Unsigned integer type. */
+    using size_type = typename pool_type::size_type;
+    /*! The type of the component iterated by the view. */
+    using raw_type = typename pool_type::type;
+
+    /**
+     * @brief Constructs a view out of a pool of components.
+     * @param pool A reference to a pool of components.
+     */
+    explicit View(pool_type &pool) noexcept
+        : pool{pool}
+    {}
+
+    /**
+     * @brief Returns the number of entities that have the given component.
+     * @return The number of entities that have the given component.
+     */
+    size_type size() const noexcept {
+        return pool.size();
+    }
+
+    /**
+     * @brief Direct access to the list of components.
+     *
+     * The returned pointer is such that range `[raw(), raw() + size()]` is
+     * always a valid range, even if the container is empty.
+     *
+     * @note
+     * There are no guarantees on the order of the components. Use `begin` and
+     * `end` if you want to iterate the view in the expected order.
+     *
+     * @return A pointer to the array of components.
+     */
+    raw_type * raw() noexcept {
+        return pool.raw();
+    }
+
+    /**
+     * @brief Direct access to the list of components.
+     *
+     * The returned pointer is such that range `[raw(), raw() + size()]` is
+     * always a valid range, even if the container is empty.
+     *
+     * @note
+     * There are no guarantees on the order of the components. Use `begin` and
+     * `end` if you want to iterate the view in the expected order.
+     *
+     * @return A pointer to the array of components.
+     */
+    const raw_type * raw() const noexcept {
+        return pool.raw();
+    }
+
+    /**
+     * @brief Direct access to the list of entities.
+     *
+     * The returned pointer is such that range `[data(), data() + size()]` is
+     * always a valid range, even if the container is empty.
+     *
+     * @note
+     * There are no guarantees on the order of the entities. Use `begin` and
+     * `end` if you want to iterate the view in the expected order.
+     *
+     * @return A pointer to the array of entities.
+     */
+    const entity_type * data() const noexcept {
+        return pool.data();
+    }
+
+    /**
+     * @brief Returns an iterator to the first entity that has the given
+     * component.
+     *
+     * The returned iterator points to the first entity that has the given
+     * component. If the view is empty, the returned iterator will be equal to
+     * `end()`.
+     *
+     * @note
+     * Input iterators stay true to the order imposed to the underlying data
+     * structures.
+     *
+     * @return An iterator to the first entity that has the given component.
+     */
+    iterator_type begin() const noexcept {
+        return pool.begin();
+    }
+
+    /**
+     * @brief Returns an iterator that is past the last entity that has the
+     * given component.
+     *
+     * The returned iterator points to the entity following the last entity that
+     * has the given component. Attempting to dereference the returned iterator
+     * results in undefined behavior.
+     *
+     * @note
+     * Input iterators stay true to the order imposed to the underlying data
+     * structures.
+     *
+     * @return An iterator to the entity following the last entity that has the
+     * given component.
+     */
+    iterator_type end() const noexcept {
+        return pool.end();
+    }
+
+    /**
+     * @brief Returns the component assigned to the given entity.
+     *
+     * Prefer this function instead of `Registry::get` during iterations. It has
+     * far better performance than its companion function.
+     *
+     * @warning
+     * Attempting to use an entity that doesn't belong to the view results in
+     * undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode if the
+     * view doesn't contain the given entity.
+     *
+     * @param entity A valid entity identifier.
+     * @return The component assigned to the entity.
+     */
+    const Component & get(entity_type entity) const noexcept {
+        return pool.get(entity);
+    }
+
+    /**
+     * @brief Returns the component assigned to the given entity.
+     *
+     * Prefer this function instead of `Registry::get` during iterations. It has
+     * far better performance than its companion function.
+     *
+     * @warning
+     * Attempting to use an entity that doesn't belong to the view results in
+     * undefined behavior.<br/>
+     * An assertion will abort the execution at runtime in debug mode if the
+     * view doesn't contain the given entity.
+     *
+     * @param entity A valid entity identifier.
+     * @return The component assigned to the entity.
+     */
+    Component & get(entity_type entity) noexcept {
+        return const_cast<Component &>(const_cast<const View *>(this)->get(entity));
+    }
+
+private:
+    pool_type &pool;
+};
+
+
+}
+
+
+#endif // ENTT_ENTITY_VIEW_HPP

src/entt/entt.hpp

@@ -0,0 +1,7 @@
+#include "core/family.hpp"
+#include "core/ident.hpp"
+#include "entity/registry.hpp"
+#include "entity/sparse_set.hpp"
+#include "entity/traits.hpp"
+#include "entity/view.hpp"
+#include "signal/sigh.hpp"

src/entt/signal/sigh.hpp

@@ -0,0 +1,348 @@
+#ifndef ENTT_SIGNAL_SIGH_HPP
+#define ENTT_SIGNAL_SIGH_HPP
+
+
+#include <algorithm>
+#include <utility>
+#include <vector>
+
+
+namespace entt {
+
+
+namespace {
+
+
+template<typename, typename>
+struct Invoker;
+
+
+template<typename Ret, typename... Args, typename Collector>
+struct Invoker<Ret(Args...), Collector> {
+    using proto_type = Ret(*)(void *, Args...);
+    using call_type = std::pair<void *, proto_type>;
+
+    virtual ~Invoker() = default;
+
+    template<typename SFINAE = Ret>
+    typename std::enable_if<std::is_void<SFINAE>::value, bool>::type
+    invoke(Collector &, proto_type proto, void *instance, Args... args) {
+        proto(instance, args...);
+        return true;
+    }
+
+    template<typename SFINAE = Ret>
+    typename std::enable_if<!std::is_void<SFINAE>::value, bool>::type
+    invoke(Collector &collector, proto_type proto, void *instance, Args... args) {
+        return collector(proto(instance, args...));
+    }
+};
+
+
+template<typename Ret>
+struct NullCollector final {
+    using result_type = Ret;
+    bool operator()(result_type) const noexcept { return true; }
+};
+
+
+template<>
+struct NullCollector<void> final {
+    using result_type = void;
+    bool operator()() const noexcept { return true; }
+};
+
+
+template<typename>
+struct DefaultCollector;
+
+
+template<typename Ret, typename... Args>
+struct DefaultCollector<Ret(Args...)> final {
+    using collector_type = NullCollector<Ret>;
+};
+
+
+template<typename Function>
+using DefaultCollectorType = typename DefaultCollector<Function>::collector_type;
+
+
+}
+
+
+/**
+ * @brief Signal handler.
+ *
+ * Primary template isn't defined on purpose. All the specializations give a
+ * compile-time error unless the template parameter is a function type.
+ */
+template<typename Function, typename = DefaultCollectorType<Function>>
+class SigH;
+
+
+/**
+ * @brief Signal handler.
+ *
+ * Unmanaged signal handler. It works directly with naked pointers to classes
+ * and pointers to member functions as well as pointers to free functions. Users
+ * of this class are in charge of disconnecting instances before deleting them.
+ *
+ * This class serves mainly two purposes:
+ * * Creating signals to be used later to notify a bunch of listeners.
+ * * Collecting results from a set of functions like in a voting system.
+ *
+ * The default collector does nothing. To properly collect data, define and use
+ * a class that has a call operator the signature of which is `bool(Param)` and:
+ * * `Param` is a type to which `Ret` can be converted.
+ * * The return type is true if the handler must stop collecting data, false
+ *   otherwise.
+ *
+ * @tparam Ret Return type of a function type.
+ * @tparam Args Types of the arguments of a function type.
+ * @tparam Collector The type of the collector to use if any.
+ */
+template<typename Ret, typename... Args, typename Collector>
+class SigH<Ret(Args...), Collector> final: private Invoker<Ret(Args...), Collector> {
+    using typename Invoker<Ret(Args...), Collector>::call_type;
+
+    template<Ret(*Function)(Args...)>
+    static Ret proto(void *, Args... args) {
+        return (Function)(args...);
+    }
+
+    template<typename Class, Ret(Class::*Member)(Args... args)>
+    static Ret proto(void *instance, Args... args) {
+        return (static_cast<Class *>(instance)->*Member)(args...);
+    }
+
+public:
+    /*! @brief Unsigned integer type. */
+    using size_type = typename std::vector<call_type>::size_type;
+    /*! @brief Collector type. */
+    using collector_type = Collector;
+
+    /*! @brief Default constructor, explicit on purpose. */
+    explicit SigH() noexcept = default;
+
+    /*! @brief Default destructor. */
+    ~SigH() noexcept = default;
+
+    /**
+     * @brief Copy constructor, listeners are also connected to this signal.
+     * @param other A signal to be used as source to initialize this instance.
+     */
+    SigH(const SigH &other)
+        : calls{other.calls}
+    {}
+
+    /**
+     * @brief Default move constructor.
+     * @param other A signal to be used as source to initialize this instance.
+     */
+    SigH(SigH &&other): SigH{} {
+        swap(*this, other);
+    }
+
+    /**
+     * @brief Assignment operator, listeners are also connected to this signal.
+     * @param other A signal to be used as source to initialize this instance.
+     * @return This signal.
+     */
+    SigH & operator=(const SigH &other) {
+        calls = other.calls;
+        return *this;
+    }
+
+    /**
+     * @brief Default move operator.
+     * @param other A signal to be used as source to initialize this instance.
+     * @return This signal.
+     */
+    SigH & operator=(SigH &&other) {
+        swap(*this, other);
+        return *this;
+    }
+
+    /**
+     * @brief The number of listeners connected to the signal.
+     * @return The number of listeners currently connected.
+     */
+    size_type size() const noexcept {
+        return calls.size();
+    }
+
+    /**
+     * @brief Returns true is at least a listener is connected to the signal.
+     * @return True if the signal has no listeners connected, false otherwise.
+     */
+    bool empty() const noexcept {
+        return calls.empty();
+    }
+
+    /**
+     * @brief Disconnects all the listeners from the signal.
+     */
+    void clear() noexcept {
+        calls.clear();
+    }
+
+    /**
+     * @brief Connects a free function to the signal.
+     *
+     * @note
+     * The signal handler performs checks to avoid multiple connections for free
+     * functions.
+     *
+     * @tparam Function A valid free function pointer.
+     */
+    template<Ret(*Function)(Args...)>
+    void connect() {
+        disconnect<Function>();
+        calls.emplace_back(nullptr, &proto<Function>);
+    }
+
+    /**
+     * @brief Connects the member function for the given instance to the signal.
+     *
+     * The signal isn't responsible for the connected object. Users must
+     * guarantee that the lifetime of the instance overcomes the one of the
+     * signal.
+     *
+     * @warning
+     * The signal handler performs checks to avoid multiple connections for the
+     * same member function of a given instance.
+     *
+     * @tparam Class The type of the class to which the member function belongs.
+     * @tparam Member The member function to connect to the signal.
+     * @param instance A valid instance of type pointer to `Class`.
+     */
+    template <typename Class, Ret(Class::*Member)(Args...)>
+    void connect(Class *instance) {
+        disconnect<Class, Member>(instance);
+        calls.emplace_back(instance, &proto<Class, Member>);
+    }
+
+    /**
+     * @brief Disconnects a free function from the signal.
+     * @tparam Function A valid free function pointer.
+     */
+    template<Ret(*Function)(Args...)>
+    void disconnect() {
+        call_type target{nullptr, &proto<Function>};
+        calls.erase(std::remove(calls.begin(), calls.end(), std::move(target)), calls.end());
+    }
+
+    /**
+     * @brief Disconnects the given member function from the signal.
+     * @tparam Class The type of the class to which the member function belongs.
+     * @tparam Member The member function to connect to the signal.
+     * @param instance A valid instance of type pointer to `Class`.
+     */
+    template<typename Class, Ret(Class::*Member)(Args...)>
+    void disconnect(Class *instance) {
+        call_type target{instance, &proto<Class, Member>};
+        calls.erase(std::remove(calls.begin(), calls.end(), std::move(target)), calls.end());
+    }
+
+    /**
+     * @brief Removes all existing connections for the given instance.
+     * @tparam Class The type of the class to which the member function belongs.
+     * @param instance A valid instance of type pointer to `Class`.
+     */
+    template<typename Class>
+    void disconnect(Class *instance) {
+        auto func = [instance](const call_type &call) { return call.first == instance; };
+        calls.erase(std::remove_if(calls.begin(), calls.end(), std::move(func)), calls.end());
+    }
+
+    /**
+     * @brief Triggers the signal.
+     *
+     * All the listeners are notified. Order isn't guaranteed.
+     *
+     * @param args Arguments to use to invoke listeners.
+     */
+    void publish(Args... args) {
+        for(auto &&call: calls) {
+            call.second(call.first, args...);
+        }
+    }
+
+    /**
+     * @brief Collects return values from the listeners.
+     * @param args Arguments to use to invoke listeners.
+     * @return An instance of the collector filled with collected data.
+     */
+    collector_type collect(Args... args) {
+        collector_type collector;
+
+        for(auto &&call: calls) {
+            if(!this->invoke(collector, call.second, call.first, args...)) {
+                break;
+            }
+        }
+
+        return collector;
+    }
+
+    /**
+     * @brief Swaps listeners between the two signals.
+     * @param lhs A valid signal object.
+     * @param rhs A valid signal object.
+     */
+    friend void swap(SigH &lhs, SigH &rhs) {
+        using std::swap;
+        swap(lhs.calls, rhs.calls);
+    }
+
+    /**
+     * @brief Checks if the contents of the two signals are identical.
+     *
+     * Two signals are identical if they have the same size and the same
+     * listeners registered exactly in the same order.
+     *
+     * @param other Signal with which to compare.
+     * @return True if the two signals are identical, false otherwise.
+     */
+    bool operator==(const SigH &other) const noexcept {
+        return (calls.size() == other.calls.size()) && std::equal(calls.cbegin(), calls.cend(), other.calls.cbegin());
+    }
+
+private:
+    std::vector<call_type> calls;
+};
+
+
+/**
+ * @brief Checks if the contents of the two signals are different.
+ *
+ * Two signals are identical if they have the same size and the same
+ * listeners registered exactly in the same order.
+ *
+ * @tparam Ret Return type of a function type.
+ * @tparam Args Types of the arguments of a function type.
+ * @param lhs A valid signal object.
+ * @param rhs A valid signal object.
+ * @return True if the two signals are different, false otherwise.
+ */
+template<typename Ret, typename... Args>
+bool operator!=(const SigH<Ret(Args...)> &lhs, const SigH<Ret(Args...)> &rhs) noexcept {
+    return !(lhs == rhs);
+}
+
+
+/**
+ * @brief Event handler.
+ *
+ * Unmanaged event handler. Collecting data for this kind of signals doesn't
+ * make sense at all. Its sole purpose is to provide the listeners with the
+ * given event.
+ */
+template<typename Event>
+using EventH = SigH<void(const Event &)>;
+
+
+}
+
+
+#endif // ENTT_SIGNAL_SIGH_HPP

src/ident.hpp

@@ -1,43 +0,0 @@
-#ifndef ENTT_IDENT_HPP
-#define ENTT_IDENT_HPP
-
-
-#include<type_traits>
-#include<cstddef>
-#include<utility>
-
-
-namespace entt {
-
-
-namespace details {
-
-
-template<typename Type>
-struct Wrapper {
-    using type = Type;
-    constexpr Wrapper(std::size_t index): index{index} {}
-    const std::size_t index;
-};
-
-template<typename... Types>
-struct Identifier final: Wrapper<Types>... {
-    template<std::size_t... Indexes>
-    constexpr Identifier(std::index_sequence<Indexes...>): Wrapper<Types>{Indexes}... {}
-
-    template<typename Type>
-    constexpr std::size_t get() const { return Wrapper<std::decay_t<Type>>::index; }
-};
-
-
-}
-
-
-template<typename... Types>
-constexpr auto ident = details::Identifier<std::decay_t<Types>...>{std::make_index_sequence<sizeof...(Types)>{}};
-
-
-}
-
-
-#endif // ENTT_IDENT_HPP

src/registry.hpp

@@ -1,414 +0,0 @@
-#ifndef ENTT_REGISTRY_HPP
-#define ENTT_REGISTRY_HPP
-
-
-#include <vector>
-#include <bitset>
-#include <utility>
-#include <cstddef>
-#include <iterator>
-#include <cassert>
-#include <type_traits>
-#include "component_pool.hpp"
-#include "ident.hpp"
-
-
-namespace entt {
-
-
-template<typename...>
-class View;
-
-
-template<template<typename...> class Pool, typename Entity, typename... Components, typename Type, typename... Types>
-class View<Pool<Entity, Components...>, Type, Types...> final {
-    using pool_type = Pool<Entity, Components...>;
-    using entity_type = typename pool_type::entity_type;
-    using mask_type = std::bitset<sizeof...(Components)+1>;
-    using underlying_iterator_type = typename pool_type::const_iterator_type;
-
-    class ViewIterator;
-
-public:
-    using iterator_type = ViewIterator;
-    using const_iterator_type = iterator_type;
-    using size_type = typename pool_type::size_type;
-
-private:
-    class ViewIterator {
-        inline bool valid() const noexcept {
-            return ((mask[*begin] & bitmask) == bitmask);
-        }
-
-    public:
-        using value_type = entity_type;
-        using difference_type = std::ptrdiff_t;
-        using reference = entity_type &;
-        using pointer = entity_type *;
-        using iterator_category = std::input_iterator_tag;
-
-        ViewIterator(underlying_iterator_type begin, underlying_iterator_type end, const mask_type &bitmask, const mask_type *mask) noexcept
-            : begin{begin}, end{end}, bitmask{bitmask}, mask{mask}
-        {
-            if(begin != end && !valid()) {
-                ++(*this);
-            }
-        }
-
-        ViewIterator & operator++() noexcept {
-            ++begin;
-            while(begin != end && !valid()) { ++begin; }
-            return *this;
-        }
-
-        ViewIterator operator++(int) noexcept {
-            ViewIterator orig = *this;
-            return ++(*this), orig;
-        }
-
-        bool operator==(const ViewIterator &other) const noexcept {
-            return other.begin == begin;
-        }
-
-        bool operator!=(const ViewIterator &other) const noexcept {
-            return !(*this == other);
-        }
-
-        value_type operator*() const noexcept {
-            return *begin;
-        }
-
-    private:
-        underlying_iterator_type begin;
-        underlying_iterator_type end;
-        const mask_type bitmask;
-        const mask_type *mask;
-    };
-
-    template<typename Comp>
-    void prefer(size_type &size) noexcept {
-        auto sz = pool.template size<Comp>();
-
-        if(sz < size) {
-            from = pool.template begin<Type>();
-            to = pool.template end<Type>();
-            size = sz;
-        }
-    }
-
-public:
-    explicit View(pool_type &pool, const mask_type *mask) noexcept
-        : from{pool.template begin<Type>()},
-          to{pool.template end<Type>()},
-          pool{pool},
-          mask{mask}
-    {
-        using accumulator_type = int[];
-        size_type size = pool.template size<Type>();
-        bitmask.set(ident<Components...>.template get<Type>());
-        accumulator_type types = { 0, (bitmask.set(ident<Components...>.template get<Types>()), 0)... };
-        accumulator_type pref = { 0, (prefer<Types>(size), 0)... };
-        (void)types, (void)pref;
-    }
-
-    const_iterator_type begin() const noexcept {
-        return ViewIterator{from, to, bitmask, mask};
-    }
-
-    iterator_type begin() noexcept {
-        return const_cast<const View *>(this)->begin();
-    }
-
-    const_iterator_type end() const noexcept {
-        return ViewIterator{to, to, bitmask, mask};
-    }
-
-    iterator_type end() noexcept {
-        return const_cast<const View *>(this)->end();
-    }
-
-    void reset() noexcept {
-        using accumulator_type = int[];
-        from = pool.template begin<Type>();
-        to = pool.template end<Type>();
-        size_type size = pool.template size<Type>();
-        accumulator_type accumulator = { 0, (prefer<Types>(size), 0)... };
-        (void)accumulator;
-    }
-
-private:
-    underlying_iterator_type from;
-    underlying_iterator_type to;
-    pool_type &pool;
-    const mask_type *mask;
-    mask_type bitmask;
-};
-
-
-template<template<typename...> class Pool, typename Entity, typename... Components, typename Type>
-class View<Pool<Entity, Components...>, Type> final {
-    using pool_type = Pool<Entity, Components...>;
-
-public:
-    using size_type = typename pool_type::size_type;
-    using iterator_type = typename pool_type::const_iterator_type;
-    using const_iterator_type = iterator_type;
-
-    explicit View(pool_type &pool) noexcept
-        : pool{pool}
-    {}
-
-    const_iterator_type cbegin() const noexcept {
-        return pool.template cbegin<Type>();
-    }
-
-    iterator_type begin() noexcept {
-        return pool.template begin<Type>();
-    }
-
-    const_iterator_type cend() const noexcept {
-        return pool.template cend<Type>();
-    }
-
-    iterator_type end() noexcept {
-        return pool.template end<Type>();
-    }
-
-    size_type size() const noexcept {
-        return pool.template size<Type>();
-    }
-
-private:
-    pool_type &pool;
-};
-
-
-template<typename>
-class Registry;
-
-
-template<template<typename...> class Pool, typename Entity, typename... Components>
-class Registry<Pool<Entity, Components...>> {
-    static_assert(sizeof...(Components) > 1, "!");
-
-    using pool_type = Pool<Entity, Components...>;
-    using mask_type = std::bitset<sizeof...(Components)+1>;
-
-    static constexpr auto validity_bit = sizeof...(Components);
-
-public:
-    using entity_type = typename pool_type::entity_type;
-    using size_type = typename std::vector<mask_type>::size_type;
-
-private:
-    template<typename Comp>
-    void clone(entity_type to, entity_type from) {
-        if(entities[from].test(ident<Components...>.template get<Comp>())) {
-            assign<Comp>(to, pool.template get<Comp>(from));
-        }
-    }
-
-    template<typename Comp>
-    void sync(entity_type to, entity_type from) {
-        bool src = entities[from].test(ident<Components...>.template get<Comp>());
-        bool dst = entities[to].test(ident<Components...>.template get<Comp>());
-
-        if(src && dst) {
-            copy<Comp>(to, from);
-        } else if(src) {
-            clone<Comp>(to, from);
-        } else if(dst) {
-            remove<Comp>(to);
-        }
-    }
-
-public:
-    template<typename... Comp>
-    using view_type = View<pool_type, Comp...>;
-
-    template<typename... Args>
-    Registry(Args&&... args)
-        : pool{std::forward<Args>(args)...}
-    {}
-
-    Registry(const Registry &) = delete;
-    Registry(Registry &&) = delete;
-
-    Registry & operator=(const Registry &) = delete;
-    Registry & operator=(Registry &&) = delete;
-
-    size_type size() const noexcept {
-        return entities.size() - available.size();
-    }
-
-    size_type capacity() const noexcept {
-        return entities.size();
-    }
-
-    template<typename Comp>
-    bool empty() const noexcept {
-        return pool.template empty<Comp>();
-    }
-
-    bool empty() const noexcept {
-        return entities.empty();
-    }
-
-    bool valid(entity_type entity) const noexcept {
-        return (entity < entities.size() && entities[entity].test(validity_bit));
-    }
-
-    template<typename... Comp>
-    entity_type create() noexcept {
-        using accumulator_type = int[];
-        auto entity = create();
-        accumulator_type accumulator = { 0, (assign<Comp>(entity), 0)... };
-        (void)accumulator;
-        return entity;
-    }
-
-    entity_type create() noexcept {
-        entity_type entity;
-
-        if(available.empty()) {
-            entity = entity_type(entities.size());
-            entities.emplace_back();
-        } else {
-            entity = available.back();
-            available.pop_back();
-        }
-
-        entities[entity].set(validity_bit);
-
-        return entity;
-    }
-
-    void destroy(entity_type entity) {
-        assert(valid(entity));
-        using accumulator_type = int[];
-        accumulator_type accumulator = { 0, (reset<Components>(entity), 0)... };
-        available.push_back(entity);
-        entities[entity].reset();
-        (void)accumulator;
-    }
-
-    template<typename Comp, typename... Args>
-    Comp & assign(entity_type entity, Args... args) {
-        assert(valid(entity));
-        entities[entity].set(ident<Components...>.template get<Comp>());
-        return pool.template construct<Comp>(entity, args...);
-    }
-
-    template<typename Comp>
-    void remove(entity_type entity) {
-        assert(valid(entity));
-        entities[entity].reset(ident<Components...>.template get<Comp>());
-        pool.template destroy<Comp>(entity);
-    }
-
-    template<typename... Comp>
-    bool has(entity_type entity) const noexcept {
-        assert(valid(entity));
-        using accumulator_type = bool[];
-        bool all = true;
-        auto &mask = entities[entity];
-        accumulator_type accumulator = { true, (all = all && mask.test(ident<Components...>.template get<Comp>()))... };
-        (void)accumulator;
-        return all;
-    }
-
-    template<typename Comp>
-    const Comp & get(entity_type entity) const noexcept {
-        return pool.template get<Comp>(entity);
-    }
-
-    template<typename Comp>
-    Comp & get(entity_type entity) noexcept {
-        return pool.template get<Comp>(entity);
-    }
-
-    template<typename Comp, typename... Args>
-    Comp & replace(entity_type entity, Args... args) {
-        return (pool.template get<Comp>(entity) = Comp{args...});
-    }
-
-    template<typename Comp, typename... Args>
-    Comp & accomodate(entity_type entity, Args... args) {
-        assert(valid(entity));
-
-        return (entities[entity].test(ident<Components...>.template get<Comp>())
-                ? this->template replace<Comp>(entity, std::forward<Args>(args)...)
-                : this->template assign<Comp>(entity, std::forward<Args>(args)...));
-    }
-
-    entity_type clone(entity_type from) {
-        assert(valid(from));
-        using accumulator_type = int[];
-        auto to = create();
-        accumulator_type accumulator = { 0, (clone<Components>(to, from), 0)... };
-        (void)accumulator;
-        return to;
-    }
-
-    template<typename Comp>
-    Comp & copy(entity_type to, entity_type from) {
-        return (pool.template get<Comp>(to) = pool.template get<Comp>(from));
-    }
-
-    void copy(entity_type to, entity_type from) {
-        using accumulator_type = int[];
-        accumulator_type accumulator = { 0, (sync<Components>(to, from), 0)... };
-        (void)accumulator;
-    }
-
-    template<typename Comp>
-    void reset(entity_type entity) {
-        assert(valid(entity));
-
-        if(entities[entity].test(ident<Components...>.template get<Comp>())) {
-            remove<Comp>(entity);
-        }
-    }
-
-    template<typename Comp>
-    void reset() {
-        for(entity_type entity = 0, last = entity_type(entities.size()); entity < last; ++entity) {
-            if(entities[entity].test(ident<Components...>.template get<Comp>())) {
-                remove<Comp>(entity);
-            }
-        }
-    }
-
-    void reset() {
-        entities.clear();
-        available.clear();
-        pool.reset();
-    }
-
-    template<typename... Comp>
-    std::enable_if_t<(sizeof...(Comp) == 1), view_type<Comp...>>
-    view() noexcept { return view_type<Comp...>{pool}; }
-
-    template<typename... Comp>
-    std::enable_if_t<(sizeof...(Comp) > 1), view_type<Comp...>>
-    view() noexcept { return view_type<Comp...>{pool, entities.data()}; }
-
-private:
-    std::vector<mask_type> entities;
-    std::vector<entity_type> available;
-    pool_type pool;
-};
-
-
-template<typename Entity, typename... Components>
-using StandardRegistry = Registry<ComponentPool<Entity, Components...>>;
-
-
-template<typename... Components>
-using DefaultRegistry = Registry<ComponentPool<std::uint32_t, Components...>>;
-
-
-}
-
-
-#endif // ENTT_REGISTRY_HPP

test/CMakeLists.txt

@@ -3,24 +3,30 @@
 #
 
 set(COMMON_LINK_LIBS gtest_main Threads::Threads)
+include_directories(${PROJECT_SRC_DIR})
 
-# List of available targets
+# Test core
 
-set(TARGET_ENTT entt)
-set(TARGET_BENCHMARK benchmark)
+add_executable(core entt/core/ident.cpp entt/core/family.cpp odr.cpp)
+target_link_libraries(core PRIVATE ${COMMON_LINK_LIBS})
+add_test(NAME core COMMAND core)
 
-# Test TARGET_ENTT
+# Test entt
 
-add_executable(${TARGET_ENTT} component_pool.cpp registry.cpp)
-target_include_directories(${TARGET_ENTT} PRIVATE ${PROJECT_SRC_DIR})
-target_link_libraries(${TARGET_ENTT} PRIVATE ${COMMON_LINK_LIBS})
-add_test(NAME ${TARGET_ENTT} COMMAND ${TARGET_ENTT})
+add_executable(entity entt/entity/registry.cpp entt/entity/sparse_set.cpp entt/entity/view.cpp odr.cpp)
+target_link_libraries(entity PRIVATE ${COMMON_LINK_LIBS})
+add_test(NAME entity COMMAND entity)
 
-# Test TARGET_BENCHMARK
+# Test benchmark
 
 IF(CMAKE_BUILD_TYPE MATCHES Release)
-    add_executable(${TARGET_BENCHMARK} benchmark.cpp)
-    target_include_directories(${TARGET_BENCHMARK} PRIVATE ${PROJECT_SRC_DIR})
-    target_link_libraries(${TARGET_BENCHMARK} PRIVATE ${COMMON_LINK_LIBS})
-    add_test(NAME ${TARGET_BENCHMARK} COMMAND ${TARGET_BENCHMARK})
+    add_executable(benchmark entt/entity/benchmark.cpp odr.cpp)
+    target_link_libraries(benchmark PRIVATE ${COMMON_LINK_LIBS})
+    add_test(NAME benchmark COMMAND benchmark)
 ENDIF()
+
+# Test signal
+
+add_executable(signal entt/signal/sigh.cpp odr.cpp)
+target_link_libraries(signal PRIVATE ${COMMON_LINK_LIBS})
+add_test(NAME signal COMMAND signal)

test/benchmark.cpp

@@ -1,409 +0,0 @@
-#include <gtest/gtest.h>
-#include <registry.hpp>
-#include <iostream>
-#include <cstddef>
-#include <chrono>
-#include <vector>
-
-struct Position {
-    uint64_t x;
-    uint64_t y;
-};
-
-struct Velocity {
-    uint64_t x;
-    uint64_t y;
-};
-
-template<std::size_t>
-struct Comp {};
-
-struct Timer final {
-    Timer(): start{std::chrono::system_clock::now()} {}
-
-    void elapsed() {
-        auto now = std::chrono::system_clock::now();
-        std::cout << std::chrono::duration<double>(now - start).count() << " seconds" << std::endl;
-    }
-
-private:
-    std::chrono::time_point<std::chrono::system_clock> start;
-};
-
-TEST(DefaultRegistry, Construct) {
-    using registry_type = entt::DefaultRegistry<Position, Velocity>;
-
-    registry_type registry;
-
-    std::cout << "Constructing 10000000 entities" << std::endl;
-
-    Timer timer;
-    for (uint64_t i = 0; i < 10000000L; i++) {
-        registry.create();
-    }
-
-    timer.elapsed();
-    registry.reset();
-}
-
-TEST(DefaultRegistry, Destroy) {
-    using registry_type = entt::DefaultRegistry<Position, Velocity>;
-
-    registry_type registry;
-    std::vector<registry_type::entity_type> entities{};
-
-    std::cout << "Destroying 10000000 entities" << std::endl;
-
-    for (uint64_t i = 0; i < 10000000L; i++) {
-        entities.push_back(registry.create());
-    }
-
-    Timer timer;
-
-    for (auto entity: entities) {
-        registry.destroy(entity);
-    }
-
-    timer.elapsed();
-}
-
-TEST(DefaultRegistry, IterateCreateDeleteSingleComponent) {
-    using registry_type = entt::DefaultRegistry<Position, Velocity>;
-
-    registry_type registry;
-
-    std::cout << "Looping 10000 times creating and deleting a random number of entities" << std::endl;
-
-    Timer timer;
-
-    for(int i = 0; i < 10000; i++) {
-        for(int j = 0; j < 10000; j++) {
-            registry.create<Position>();
-        }
-
-        auto view = registry.view<Position>();
-
-        for(auto entity: view) {
-            if(rand() % 2 == 0) {
-                registry.destroy(entity);
-            }
-        }
-    }
-
-    timer.elapsed();
-    registry.reset();
-}
-
-TEST(DefaultRegistry, IterateSingleComponent10M) {
-    using registry_type = entt::DefaultRegistry<Position, Velocity>;
-
-    registry_type registry;
-
-    std::cout << "Iterating over 10000000 entities, one component" << std::endl;
-
-    for (uint64_t i = 0; i < 10000000L; i++) {
-        registry.create<Position>();
-    }
-
-    Timer timer;
-
-    auto view = registry.view<Position>();
-
-    for(auto entity: view) {
-        auto &position = registry.get<Position>(entity);
-        (void)position;
-    }
-
-    timer.elapsed();
-    registry.reset();
-}
-
-TEST(DefaultRegistry, IterateTwoComponents10M) {
-    using registry_type = entt::DefaultRegistry<Position, Velocity>;
-
-    registry_type registry;
-
-    std::cout << "Iterating over 10000000 entities, two components" << std::endl;
-
-    for (uint64_t i = 0; i < 10000000L; i++) {
-        registry.create<Position, Velocity>();
-    }
-
-    Timer timer;
-
-    auto view = registry.view<Position, Velocity>();
-
-    for(auto entity: view) {
-        auto &position = registry.get<Position>(entity);
-        auto &velocity = registry.get<Velocity>(entity);
-        (void)position;
-        (void)velocity;
-    }
-
-    timer.elapsed();
-    registry.reset();
-}
-
-TEST(DefaultRegistry, IterateTwoComponents10MHalf) {
-    using registry_type = entt::DefaultRegistry<Position, Velocity>;
-
-    registry_type registry;
-
-    std::cout << "Iterating over 10000000 entities, two components, half of the entities have all the components" << std::endl;
-
-    for (uint64_t i = 0; i < 10000000L; i++) {
-        auto entity = registry.create<Velocity>();
-        if(i % 2) { registry.assign<Position>(entity); }
-    }
-
-    Timer timer;
-
-    auto view = registry.view<Position, Velocity>();
-
-    for(auto entity: view) {
-        auto &position = registry.get<Position>(entity);
-        auto &velocity = registry.get<Velocity>(entity);
-        (void)position;
-        (void)velocity;
-    }
-
-    timer.elapsed();
-    registry.reset();
-}
-
-TEST(DefaultRegistry, IterateTwoComponents10MOne) {
-    using registry_type = entt::DefaultRegistry<Position, Velocity>;
-
-    registry_type registry;
-
-    std::cout << "Iterating over 10000000 entities, two components, only one entity has all the components" << std::endl;
-
-    for (uint64_t i = 0; i < 10000000L; i++) {
-        auto entity = registry.create<Velocity>();
-        if(i == 5000000L) { registry.assign<Position>(entity); }
-    }
-
-    Timer timer;
-
-    auto view = registry.view<Position, Velocity>();
-
-    for(auto entity: view) {
-        auto &position = registry.get<Position>(entity);
-        auto &velocity = registry.get<Velocity>(entity);
-        (void)position;
-        (void)velocity;
-    }
-
-    timer.elapsed();
-    registry.reset();
-}
-
-TEST(DefaultRegistry, IterateSingleComponent50M) {
-    using registry_type = entt::DefaultRegistry<Position, Velocity>;
-
-    registry_type registry;
-
-    std::cout << "Iterating over 50000000 entities, one component" << std::endl;
-
-    for (uint64_t i = 0; i < 50000000L; i++) {
-        registry.create<Position>();
-    }
-
-    Timer timer;
-
-    auto view = registry.view<Position>();
-
-    for(auto entity: view) {
-        auto &position = registry.get<Position>(entity);
-        (void)position;
-    }
-
-    timer.elapsed();
-    registry.reset();
-}
-
-TEST(DefaultRegistry, IterateTwoComponents50M) {
-    using registry_type = entt::DefaultRegistry<Position, Velocity>;
-
-    registry_type registry;
-
-    std::cout << "Iterating over 50000000 entities, two components" << std::endl;
-
-    for (uint64_t i = 0; i < 50000000L; i++) {
-        registry.create<Position, Velocity>();
-    }
-
-    Timer timer;
-
-    auto view = registry.view<Position, Velocity>();
-
-    for(auto entity: view) {
-        auto &position = registry.get<Position>(entity);
-        auto &velocity = registry.get<Velocity>(entity);
-        (void)position;
-        (void)velocity;
-    }
-
-    timer.elapsed();
-    registry.reset();
-}
-
-TEST(DefaultRegistry, IterateFiveComponents10M) {
-    using registry_type = entt::DefaultRegistry<Position, Velocity, Comp<1>, Comp<2>, Comp<3>>;
-
-    registry_type registry;
-
-    std::cout << "Iterating over 10000000 entities, five components" << std::endl;
-
-    for (uint64_t i = 0; i < 10000000L; i++) {
-        registry.create<Position, Velocity, Comp<1>, Comp<2>, Comp<3>>();
-    }
-
-    Timer timer;
-
-    auto view = registry.view<Position, Velocity, Comp<1>, Comp<2>, Comp<3>>();
-
-    for(auto entity: view) {
-        auto &position = registry.get<Position>(entity);
-        auto &velocity = registry.get<Velocity>(entity);
-        auto &comp1 = registry.get<Comp<1>>(entity);
-        auto &comp2 = registry.get<Comp<2>>(entity);
-        auto &comp3 = registry.get<Comp<3>>(entity);
-        (void)position;
-        (void)velocity;
-        (void)comp1;
-        (void)comp2;
-        (void)comp3;
-    }
-
-    timer.elapsed();
-    registry.reset();
-}
-
-TEST(DefaultRegistry, IterateTenComponents10M) {
-    using registry_type = entt::DefaultRegistry<Position, Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>;
-
-    registry_type registry;
-
-    std::cout << "Iterating over 10000000 entities, ten components" << std::endl;
-
-    for (uint64_t i = 0; i < 10000000L; i++) {
-        registry.create<Position, Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>();
-    }
-
-    Timer timer;
-
-    auto view = registry.view<Position, Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>();
-
-    for(auto entity: view) {
-        auto &position = registry.get<Position>(entity);
-        auto &velocity = registry.get<Velocity>(entity);
-        auto &comp1 = registry.get<Comp<1>>(entity);
-        auto &comp2 = registry.get<Comp<2>>(entity);
-        auto &comp3 = registry.get<Comp<3>>(entity);
-        auto &comp4 = registry.get<Comp<4>>(entity);
-        auto &comp5 = registry.get<Comp<5>>(entity);
-        auto &comp6 = registry.get<Comp<6>>(entity);
-        auto &comp7 = registry.get<Comp<7>>(entity);
-        auto &comp8 = registry.get<Comp<8>>(entity);
-        (void)position;
-        (void)velocity;
-        (void)comp1;
-        (void)comp2;
-        (void)comp3;
-        (void)comp4;
-        (void)comp5;
-        (void)comp6;
-        (void)comp7;
-        (void)comp8;
-    }
-
-    timer.elapsed();
-    registry.reset();
-}
-
-TEST(DefaultRegistry, IterateTenComponents10MHalf) {
-    using registry_type = entt::DefaultRegistry<Position, Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>;
-
-    registry_type registry;
-
-    std::cout << "Iterating over 10000000 entities, ten components, half of the entities have all the components" << std::endl;
-
-    for (uint64_t i = 0; i < 10000000L; i++) {
-        auto entity = registry.create<Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>();
-        if(i % 2) { registry.assign<Position>(entity); }
-    }
-
-    Timer timer;
-
-    auto view = registry.view<Position, Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>();
-
-    for(auto entity: view) {
-        auto &position = registry.get<Position>(entity);
-        auto &velocity = registry.get<Velocity>(entity);
-        auto &comp1 = registry.get<Comp<1>>(entity);
-        auto &comp2 = registry.get<Comp<2>>(entity);
-        auto &comp3 = registry.get<Comp<3>>(entity);
-        auto &comp4 = registry.get<Comp<4>>(entity);
-        auto &comp5 = registry.get<Comp<5>>(entity);
-        auto &comp6 = registry.get<Comp<6>>(entity);
-        auto &comp7 = registry.get<Comp<7>>(entity);
-        auto &comp8 = registry.get<Comp<8>>(entity);
-        (void)position;
-        (void)velocity;
-        (void)comp1;
-        (void)comp2;
-        (void)comp3;
-        (void)comp4;
-        (void)comp5;
-        (void)comp6;
-        (void)comp7;
-        (void)comp8;
-    }
-
-    timer.elapsed();
-    registry.reset();
-}
-
-TEST(DefaultRegistry, IterateTenComponents10MOne) {
-    using registry_type = entt::DefaultRegistry<Position, Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>;
-
-    registry_type registry;
-
-    std::cout << "Iterating over 10000000 entities, ten components, only one entity has all the components" << std::endl;
-
-    for (uint64_t i = 0; i < 10000000L; i++) {
-        auto entity = registry.create<Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>();
-        if(i == 5000000L) { registry.assign<Position>(entity); }
-    }
-
-    Timer timer;
-
-    auto view = registry.view<Position, Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>();
-
-    for(auto entity: view) {
-        auto &position = registry.get<Position>(entity);
-        auto &velocity = registry.get<Velocity>(entity);
-        auto &comp1 = registry.get<Comp<1>>(entity);
-        auto &comp2 = registry.get<Comp<2>>(entity);
-        auto &comp3 = registry.get<Comp<3>>(entity);
-        auto &comp4 = registry.get<Comp<4>>(entity);
-        auto &comp5 = registry.get<Comp<5>>(entity);
-        auto &comp6 = registry.get<Comp<6>>(entity);
-        auto &comp7 = registry.get<Comp<7>>(entity);
-        auto &comp8 = registry.get<Comp<8>>(entity);
-        (void)position;
-        (void)velocity;
-        (void)comp1;
-        (void)comp2;
-        (void)comp3;
-        (void)comp4;
-        (void)comp5;
-        (void)comp6;
-        (void)comp7;
-        (void)comp8;
-    }
-
-    timer.elapsed();
-    registry.reset();
-}

test/component_pool.cpp

@@ -1,166 +0,0 @@
-#include <cstddef>
-#include <gtest/gtest.h>
-#include <component_pool.hpp>
-
-TEST(ComponentPool, Functionalities) {
-    using pool_type = entt::ComponentPool<std::uint8_t, int, double>;
-
-    pool_type pool{0};
-
-    ASSERT_TRUE(pool.empty<int>());
-    ASSERT_TRUE(pool.empty<double>());
-    ASSERT_EQ(pool.capacity<int>(), pool_type::size_type{0});
-    ASSERT_EQ(pool.capacity<double>(), pool_type::size_type{0});
-    ASSERT_EQ(pool.size<int>(), pool_type::size_type{0});
-    ASSERT_EQ(pool.size<double>(), pool_type::size_type{0});
-    ASSERT_EQ(pool.begin<int>(), pool.end<int>());
-    ASSERT_EQ(pool.begin<double>(), pool.end<double>());
-    ASSERT_FALSE(pool.has<int>(0));
-    ASSERT_FALSE(pool.has<double>(0));
-}
-
-TEST(ComponentPool, ConstructDestroy) {
-    using pool_type = entt::ComponentPool<std::uint8_t, double, int>;
-
-    pool_type pool{4};
-
-    ASSERT_EQ(pool.construct<int>(0, 42), 42);
-    ASSERT_FALSE(pool.empty<int>());
-    ASSERT_TRUE(pool.empty<double>());
-    ASSERT_EQ(pool.capacity<int>(), pool_type::size_type{4});
-    ASSERT_EQ(pool.capacity<double>(), pool_type::size_type{4});
-    ASSERT_EQ(pool.size<int>(), pool_type::size_type{1});
-    ASSERT_EQ(pool.size<double>(), pool_type::size_type{0});
-    ASSERT_TRUE(pool.has<int>(0));
-    ASSERT_FALSE(pool.has<double>(0));
-    ASSERT_FALSE(pool.has<int>(1));
-    ASSERT_FALSE(pool.has<double>(1));
-
-    ASSERT_EQ(pool.construct<int>(1), 0);
-    ASSERT_FALSE(pool.empty<int>());
-    ASSERT_TRUE(pool.empty<double>());
-    ASSERT_EQ(pool.capacity<int>(), pool_type::size_type{4});
-    ASSERT_EQ(pool.capacity<double>(), pool_type::size_type{4});
-    ASSERT_EQ(pool.size<int>(), pool_type::size_type{2});
-    ASSERT_EQ(pool.size<double>(), pool_type::size_type{0});
-    ASSERT_TRUE(pool.has<int>(0));
-    ASSERT_FALSE(pool.has<double>(0));
-    ASSERT_TRUE(pool.has<int>(1));
-    ASSERT_FALSE(pool.has<double>(1));
-    ASSERT_NE(pool.get<int>(0), pool.get<int>(1));
-    ASSERT_NE(&pool.get<int>(0), &pool.get<int>(1));
-
-    ASSERT_NO_THROW(pool.destroy<int>(0));
-    ASSERT_FALSE(pool.empty<int>());
-    ASSERT_TRUE(pool.empty<double>());
-    ASSERT_EQ(pool.capacity<int>(), pool_type::size_type{4});
-    ASSERT_EQ(pool.capacity<double>(), pool_type::size_type{4});
-    ASSERT_EQ(pool.size<int>(), pool_type::size_type{1});
-    ASSERT_EQ(pool.size<double>(), pool_type::size_type{0});
-    ASSERT_FALSE(pool.has<int>(0));
-    ASSERT_FALSE(pool.has<double>(0));
-    ASSERT_TRUE(pool.has<int>(1));
-    ASSERT_FALSE(pool.has<double>(1));
-
-    ASSERT_NO_THROW(pool.destroy<int>(1));
-    ASSERT_TRUE(pool.empty<int>());
-    ASSERT_TRUE(pool.empty<double>());
-    ASSERT_EQ(pool.capacity<int>(), pool_type::size_type{4});
-    ASSERT_EQ(pool.capacity<double>(), pool_type::size_type{4});
-    ASSERT_EQ(pool.size<int>(), pool_type::size_type{0});
-    ASSERT_EQ(pool.size<int>(), pool_type::size_type{0});
-    ASSERT_FALSE(pool.has<int>(0));
-    ASSERT_FALSE(pool.has<double>(0));
-    ASSERT_FALSE(pool.has<int>(1));
-    ASSERT_FALSE(pool.has<double>(1));
-
-    int *comp[] = {
-        &pool.construct<int>(0, 0),
-        &pool.construct<int>(1, 1),
-        nullptr,
-        &pool.construct<int>(3, 3)
-    };
-
-    ASSERT_FALSE(pool.empty<int>());
-    ASSERT_TRUE(pool.empty<double>());
-    ASSERT_EQ(pool.capacity<int>(), pool_type::size_type{4});
-    ASSERT_EQ(pool.capacity<double>(), pool_type::size_type{4});
-    ASSERT_EQ(pool.size<int>(), pool_type::size_type{3});
-    ASSERT_EQ(pool.size<double>(), pool_type::size_type{0});
-    ASSERT_TRUE(pool.has<int>(0));
-    ASSERT_FALSE(pool.has<double>(0));
-    ASSERT_TRUE(pool.has<int>(1));
-    ASSERT_FALSE(pool.has<double>(1));
-    ASSERT_FALSE(pool.has<int>(2));
-    ASSERT_FALSE(pool.has<double>(2));
-    ASSERT_TRUE(pool.has<int>(3));
-    ASSERT_FALSE(pool.has<double>(3));
-    ASSERT_EQ(&pool.get<int>(0), comp[0]);
-    ASSERT_EQ(&pool.get<int>(1), comp[1]);
-    ASSERT_EQ(&pool.get<int>(3), comp[3]);
-    ASSERT_EQ(pool.get<int>(0), 0);
-    ASSERT_EQ(pool.get<int>(1), 1);
-    ASSERT_EQ(pool.get<int>(3), 3);
-
-    ASSERT_NO_THROW(pool.destroy<int>(0));
-    ASSERT_NO_THROW(pool.destroy<int>(1));
-    ASSERT_NO_THROW(pool.destroy<int>(3));
-}
-
-TEST(ComponentPool, HasGet) {
-    using pool_type = entt::ComponentPool<std::uint8_t, int, char>;
-
-    pool_type pool;
-    const pool_type &cpool = pool;
-
-    int &comp = pool.construct<int>(0, 42);
-
-    ASSERT_EQ(pool.get<int>(0), comp);
-    ASSERT_EQ(pool.get<int>(0), 42);
-    ASSERT_TRUE(pool.has<int>(0));
-
-    ASSERT_EQ(cpool.get<int>(0), comp);
-    ASSERT_EQ(cpool.get<int>(0), 42);
-    ASSERT_TRUE(cpool.has<int>(0));
-
-    ASSERT_NO_THROW(pool.destroy<int>(0));
-}
-
-TEST(ComponentPool, BeginEndReset) {
-    using pool_type = entt::ComponentPool<std::uint8_t, int, char>;
-
-    pool_type pool{2};
-
-    ASSERT_EQ(pool.construct<int>(0, 0), 0);
-    ASSERT_EQ(pool.construct<int>(2, 2), 2);
-    ASSERT_EQ(pool.construct<int>(3, 3), 3);
-    ASSERT_EQ(pool.construct<int>(1, 1), 1);
-
-    ASSERT_EQ(pool.size<int>(), decltype(pool.size<int>()){4});
-    ASSERT_EQ(*(pool.begin<int>()+0), typename pool_type::entity_type{0});
-    ASSERT_EQ(*(pool.begin<int>()+1), typename pool_type::entity_type{2});
-    ASSERT_EQ(*(pool.begin<int>()+2), typename pool_type::entity_type{3});
-    ASSERT_EQ(*(pool.begin<int>()+3), typename pool_type::entity_type{1});
-
-    pool.destroy<int>(2);
-
-    ASSERT_EQ(pool.size<int>(), decltype(pool.size<int>()){3});
-    ASSERT_EQ(*(pool.begin<int>()+0), typename pool_type::entity_type{0});
-    ASSERT_EQ(*(pool.begin<int>()+1), typename pool_type::entity_type{1});
-    ASSERT_EQ(*(pool.begin<int>()+2), typename pool_type::entity_type{3});
-
-    ASSERT_EQ(pool.construct<char>(0, 'c'), 'c');
-
-    ASSERT_FALSE(pool.empty<int>());
-    ASSERT_FALSE(pool.empty<char>());
-
-    ASSERT_NO_THROW(pool.reset<char>());
-
-    ASSERT_FALSE(pool.empty<int>());
-    ASSERT_TRUE(pool.empty<char>());
-
-    ASSERT_NO_THROW(pool.reset());
-
-    ASSERT_TRUE(pool.empty<int>());
-    ASSERT_TRUE(pool.empty<char>());
-}

test/entt/core/family.cpp

@@ -0,0 +1,16 @@
+#include <gtest/gtest.h>
+#include <entt/core/family.hpp>
+
+using my_family = entt::Family<struct MyFamily>;
+using your_family = entt::Family<struct YourFamily>;
+
+TEST(Family, Functionalities) {
+    auto myFamilyType = my_family::type<struct MyFamilyType>();
+    auto mySameFamilyType = my_family::type<struct MyFamilyType>();
+    auto myOtherFamilyType = my_family::type<struct MyOtherFamilyType>();
+    auto yourFamilyType = your_family::type<struct YourFamilyType>();
+
+    ASSERT_EQ(myFamilyType, mySameFamilyType);
+    ASSERT_NE(myFamilyType, myOtherFamilyType);
+    ASSERT_EQ(myFamilyType, yourFamilyType);
+}

test/entt/core/ident.cpp

@@ -0,0 +1,26 @@
+#include <gtest/gtest.h>
+#include <entt/core/ident.hpp>
+
+struct A {};
+struct B {};
+
+TEST(Identifier, Uniqueness) {
+    constexpr auto ID = entt::ident<A, B>;
+    constexpr A a;
+    constexpr B b;
+
+    ASSERT_NE(ID.get<A>(), ID.get<B>());
+    ASSERT_EQ(ID.get<A>(), ID.get<decltype(a)>());
+    ASSERT_NE(ID.get<A>(), ID.get<decltype(b)>());
+    ASSERT_EQ(ID.get<A>(), ID.get<A>());
+    ASSERT_EQ(ID.get<B>(), ID.get<B>());
+
+    // test uses in constant expressions
+    switch(ID.get<B>()) {
+    case ID.get<A>():
+        FAIL();
+        break;
+    case ID.get<B>():
+        SUCCEED();
+    }
+}

test/entt/entity/benchmark.cpp

@@ -0,0 +1,667 @@
+#include <gtest/gtest.h>
+#include <iostream>
+#include <cstddef>
+#include <chrono>
+#include <vector>
+#include <entt/entity/registry.hpp>
+
+struct Position {
+    uint64_t x;
+    uint64_t y;
+};
+
+struct Velocity {
+    uint64_t x;
+    uint64_t y;
+};
+
+template<std::size_t>
+struct Comp {};
+
+struct Timer final {
+    Timer(): start{std::chrono::system_clock::now()} {}
+
+    void elapsed() {
+        auto now = std::chrono::system_clock::now();
+        std::cout << std::chrono::duration<double>(now - start).count() << " seconds" << std::endl;
+    }
+
+private:
+    std::chrono::time_point<std::chrono::system_clock> start;
+};
+
+TEST(DefaultRegistry, Construct) {
+    entt::DefaultRegistry registry;
+
+    std::cout << "Constructing 10000000 entities" << std::endl;
+
+    Timer timer;
+
+    for (uint64_t i = 0; i < 10000000L; i++) {
+        registry.create();
+    }
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, Destroy) {
+    entt::DefaultRegistry registry;
+    std::vector<entt::DefaultRegistry::entity_type> entities{};
+
+    std::cout << "Destroying 10000000 entities" << std::endl;
+
+    for (uint64_t i = 0; i < 10000000L; i++) {
+        entities.push_back(registry.create());
+    }
+
+    Timer timer;
+
+    for (auto entity: entities) {
+        registry.destroy(entity);
+    }
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, IterateCreateDeleteSingleComponent) {
+    entt::DefaultRegistry registry;
+
+    std::cout << "Looping 10000 times creating and deleting a random number of entities" << std::endl;
+
+    Timer timer;
+
+    auto view = registry.view<Position>();
+
+    for(int i = 0; i < 10000; i++) {
+        for(int j = 0; j < 10000; j++) {
+            registry.create<Position>();
+        }
+
+        for(auto entity: view) {
+            if(rand() % 2 == 0) {
+                registry.destroy(entity);
+            }
+        }
+    }
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, IterateSingleComponent10M) {
+    entt::DefaultRegistry registry;
+
+    std::cout << "Iterating over 10000000 entities, one component" << std::endl;
+
+    for (uint64_t i = 0; i < 10000000L; i++) {
+        registry.create<Position>();
+    }
+
+    Timer timer;
+
+    auto view = registry.view<Position>();
+
+    for(auto entity: view) {
+        auto &position = view.get(entity);
+        (void)position;
+    }
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, IterateTwoComponents10M) {
+    entt::DefaultRegistry registry;
+
+    std::cout << "Iterating over 10000000 entities, two components" << std::endl;
+
+    for (uint64_t i = 0; i < 10000000L; i++) {
+        registry.create<Position, Velocity>();
+    }
+
+    Timer timer;
+
+    auto view = registry.view<Position, Velocity>();
+
+    for(auto entity: view) {
+        auto &position = view.get<Position>(entity);
+        auto &velocity = view.get<Velocity>(entity);
+        (void)position;
+        (void)velocity;
+    }
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, IterateTwoComponents10MHalf) {
+    entt::DefaultRegistry registry;
+
+    std::cout << "Iterating over 10000000 entities, two components, half of the entities have all the components" << std::endl;
+
+    for (uint64_t i = 0; i < 10000000L; i++) {
+        auto entity = registry.create<Velocity>();
+        if(i % 2) { registry.assign<Position>(entity); }
+    }
+
+    Timer timer;
+
+    auto view = registry.view<Position, Velocity>();
+
+    for(auto entity: view) {
+        auto &position = view.get<Position>(entity);
+        auto &velocity = view.get<Velocity>(entity);
+        (void)position;
+        (void)velocity;
+    }
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, IterateTwoComponents10MOne) {
+    entt::DefaultRegistry registry;
+
+    std::cout << "Iterating over 10000000 entities, two components, only one entity has all the components" << std::endl;
+
+    for (uint64_t i = 0; i < 10000000L; i++) {
+        auto entity = registry.create<Velocity>();
+        if(i == 5000000L) { registry.assign<Position>(entity); }
+    }
+
+    Timer timer;
+
+    auto view = registry.view<Position, Velocity>();
+
+    for(auto entity: view) {
+        auto &position = view.get<Position>(entity);
+        auto &velocity = view.get<Velocity>(entity);
+        (void)position;
+        (void)velocity;
+    }
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, IterateTwoComponentsPersistent10M) {
+    entt::DefaultRegistry registry;
+    registry.prepare<Position, Velocity>();
+
+    std::cout << "Iterating over 10000000 entities, two components, persistent view" << std::endl;
+
+    for (uint64_t i = 0; i < 10000000L; i++) {
+        registry.create<Position, Velocity>();
+    }
+
+    Timer timer;
+
+    auto view = registry.persistent<Position, Velocity>();
+
+    for(auto entity: view) {
+        auto &position = view.get<Position>(entity);
+        auto &velocity = view.get<Velocity>(entity);
+        (void)position;
+        (void)velocity;
+    }
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, IterateTwoComponentsPersistent10MHalf) {
+    entt::DefaultRegistry registry;
+    registry.prepare<Position, Velocity>();
+
+    std::cout << "Iterating over 10000000 entities, two components, persistent view, half of the entities have all the components" << std::endl;
+
+    for (uint64_t i = 0; i < 10000000L; i++) {
+        auto entity = registry.create<Velocity>();
+        if(i % 2) { registry.assign<Position>(entity); }
+    }
+
+    Timer timer;
+
+    auto view = registry.persistent<Position, Velocity>();
+
+    for(auto entity: view) {
+        auto &position = view.get<Position>(entity);
+        auto &velocity = view.get<Velocity>(entity);
+        (void)position;
+        (void)velocity;
+    }
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, IterateTwoComponentsPersistent10MOne) {
+    entt::DefaultRegistry registry;
+    registry.prepare<Position, Velocity>();
+
+    std::cout << "Iterating over 10000000 entities, two components, persistent view, only one entity has all the components" << std::endl;
+
+    for (uint64_t i = 0; i < 10000000L; i++) {
+        auto entity = registry.create<Velocity>();
+        if(i == 5000000L) { registry.assign<Position>(entity); }
+    }
+
+    Timer timer;
+
+    auto view = registry.persistent<Position, Velocity>();
+
+    for(auto entity: view) {
+        auto &position = view.get<Position>(entity);
+        auto &velocity = view.get<Velocity>(entity);
+        (void)position;
+        (void)velocity;
+    }
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, IterateSingleComponent50M) {
+    entt::Registry<std::uint64_t> registry;
+
+    std::cout << "Iterating over 50000000 entities, one component" << std::endl;
+
+    for (uint64_t i = 0; i < 50000000L; i++) {
+        registry.create<Position>();
+    }
+
+    Timer timer;
+
+    auto view = registry.view<Position>();
+
+    for(auto entity: view) {
+        auto &position = view.get(entity);
+        (void)position;
+    }
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, IterateTwoComponents50M) {
+    entt::Registry<std::uint64_t> registry;
+
+    std::cout << "Iterating over 50000000 entities, two components" << std::endl;
+
+    for (uint64_t i = 0; i < 50000000L; i++) {
+        registry.create<Position, Velocity>();
+    }
+
+    Timer timer;
+
+    auto view = registry.view<Position, Velocity>();
+
+    for(auto entity: view) {
+        auto &position = view.get<Position>(entity);
+        auto &velocity = view.get<Velocity>(entity);
+        (void)position;
+        (void)velocity;
+    }
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, IterateTwoComponentsPersistent50M) {
+    entt::Registry<std::uint64_t> registry;
+    registry.prepare<Position, Velocity>();
+
+    std::cout << "Iterating over 50000000 entities, two components, persistent view" << std::endl;
+
+    for (uint64_t i = 0; i < 50000000L; i++) {
+        registry.create<Position, Velocity>();
+    }
+
+    Timer timer;
+
+    auto view = registry.persistent<Position, Velocity>();
+
+    for(auto entity: view) {
+        auto &position = view.get<Position>(entity);
+        auto &velocity = view.get<Velocity>(entity);
+        (void)position;
+        (void)velocity;
+    }
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, IterateFiveComponents10M) {
+    entt::DefaultRegistry registry;
+
+    std::cout << "Iterating over 10000000 entities, five components" << std::endl;
+
+    for (uint64_t i = 0; i < 10000000L; i++) {
+        registry.create<Position, Velocity, Comp<1>, Comp<2>, Comp<3>>();
+    }
+
+    Timer timer;
+
+    auto view = registry.view<Position, Velocity, Comp<1>, Comp<2>, Comp<3>>();
+
+    for(auto entity: view) {
+        auto &position = view.get<Position>(entity);
+        auto &velocity = view.get<Velocity>(entity);
+        auto &comp1 = view.get<Comp<1>>(entity);
+        auto &comp2 = view.get<Comp<2>>(entity);
+        auto &comp3 = view.get<Comp<3>>(entity);
+        (void)position;
+        (void)velocity;
+        (void)comp1;
+        (void)comp2;
+        (void)comp3;
+    }
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, IterateTenComponents10M) {
+    entt::DefaultRegistry registry;
+
+    std::cout << "Iterating over 10000000 entities, ten components" << std::endl;
+
+    for (uint64_t i = 0; i < 10000000L; i++) {
+        registry.create<Position, Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>();
+    }
+
+    Timer timer;
+
+    auto view = registry.view<Position, Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>();
+
+    for(auto entity: view) {
+        auto &position = view.get<Position>(entity);
+        auto &velocity = view.get<Velocity>(entity);
+        auto &comp1 = view.get<Comp<1>>(entity);
+        auto &comp2 = view.get<Comp<2>>(entity);
+        auto &comp3 = view.get<Comp<3>>(entity);
+        auto &comp4 = view.get<Comp<4>>(entity);
+        auto &comp5 = view.get<Comp<5>>(entity);
+        auto &comp6 = view.get<Comp<6>>(entity);
+        auto &comp7 = view.get<Comp<7>>(entity);
+        auto &comp8 = view.get<Comp<8>>(entity);
+        (void)position;
+        (void)velocity;
+        (void)comp1;
+        (void)comp2;
+        (void)comp3;
+        (void)comp4;
+        (void)comp5;
+        (void)comp6;
+        (void)comp7;
+        (void)comp8;
+    }
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, IterateTenComponents10MHalf) {
+    entt::DefaultRegistry registry;
+
+    std::cout << "Iterating over 10000000 entities, ten components, half of the entities have all the components" << std::endl;
+
+    for (uint64_t i = 0; i < 10000000L; i++) {
+        auto entity = registry.create<Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>();
+        if(i % 2) { registry.assign<Position>(entity); }
+    }
+
+    Timer timer;
+
+    auto view = registry.view<Position, Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>();
+
+    for(auto entity: view) {
+        auto &position = view.get<Position>(entity);
+        auto &velocity = view.get<Velocity>(entity);
+        auto &comp1 = view.get<Comp<1>>(entity);
+        auto &comp2 = view.get<Comp<2>>(entity);
+        auto &comp3 = view.get<Comp<3>>(entity);
+        auto &comp4 = view.get<Comp<4>>(entity);
+        auto &comp5 = view.get<Comp<5>>(entity);
+        auto &comp6 = view.get<Comp<6>>(entity);
+        auto &comp7 = view.get<Comp<7>>(entity);
+        auto &comp8 = view.get<Comp<8>>(entity);
+        (void)position;
+        (void)velocity;
+        (void)comp1;
+        (void)comp2;
+        (void)comp3;
+        (void)comp4;
+        (void)comp5;
+        (void)comp6;
+        (void)comp7;
+        (void)comp8;
+    }
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, IterateTenComponents10MOne) {
+    entt::DefaultRegistry registry;
+
+    std::cout << "Iterating over 10000000 entities, ten components, only one entity has all the components" << std::endl;
+
+    for (uint64_t i = 0; i < 10000000L; i++) {
+        auto entity = registry.create<Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>();
+        if(i == 5000000L) { registry.assign<Position>(entity); }
+    }
+
+    Timer timer;
+
+    auto view = registry.view<Position, Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>();
+
+    for(auto entity: view) {
+        auto &position = view.get<Position>(entity);
+        auto &velocity = view.get<Velocity>(entity);
+        auto &comp1 = view.get<Comp<1>>(entity);
+        auto &comp2 = view.get<Comp<2>>(entity);
+        auto &comp3 = view.get<Comp<3>>(entity);
+        auto &comp4 = view.get<Comp<4>>(entity);
+        auto &comp5 = view.get<Comp<5>>(entity);
+        auto &comp6 = view.get<Comp<6>>(entity);
+        auto &comp7 = view.get<Comp<7>>(entity);
+        auto &comp8 = view.get<Comp<8>>(entity);
+        (void)position;
+        (void)velocity;
+        (void)comp1;
+        (void)comp2;
+        (void)comp3;
+        (void)comp4;
+        (void)comp5;
+        (void)comp6;
+        (void)comp7;
+        (void)comp8;
+    }
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, IterateFiveComponentsPersistent10M) {
+    entt::DefaultRegistry registry;
+    registry.prepare<Position, Velocity, Comp<1>, Comp<2>, Comp<3>>();
+
+    std::cout << "Iterating over 10000000 entities, five components, persistent view" << std::endl;
+
+    for (uint64_t i = 0; i < 10000000L; i++) {
+        registry.create<Position, Velocity, Comp<1>, Comp<2>, Comp<3>>();
+    }
+
+    Timer timer;
+
+    auto view = registry.persistent<Position, Velocity, Comp<1>, Comp<2>, Comp<3>>();
+
+    for(auto entity: view) {
+        auto &position = view.get<Position>(entity);
+        auto &velocity = view.get<Velocity>(entity);
+        auto &comp1 = view.get<Comp<1>>(entity);
+        auto &comp2 = view.get<Comp<2>>(entity);
+        auto &comp3 = view.get<Comp<3>>(entity);
+        (void)position;
+        (void)velocity;
+        (void)comp1;
+        (void)comp2;
+        (void)comp3;
+    }
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, IterateTenComponentsPersistent10M) {
+    entt::DefaultRegistry registry;
+    registry.prepare<Position, Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>();
+
+    std::cout << "Iterating over 10000000 entities, ten components, persistent view" << std::endl;
+
+    for (uint64_t i = 0; i < 10000000L; i++) {
+        registry.create<Position, Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>();
+    }
+
+    Timer timer;
+
+    auto view = registry.persistent<Position, Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>();
+
+    for(auto entity: view) {
+        auto &position = view.get<Position>(entity);
+        auto &velocity = view.get<Velocity>(entity);
+        auto &comp1 = view.get<Comp<1>>(entity);
+        auto &comp2 = view.get<Comp<2>>(entity);
+        auto &comp3 = view.get<Comp<3>>(entity);
+        auto &comp4 = view.get<Comp<4>>(entity);
+        auto &comp5 = view.get<Comp<5>>(entity);
+        auto &comp6 = view.get<Comp<6>>(entity);
+        auto &comp7 = view.get<Comp<7>>(entity);
+        auto &comp8 = view.get<Comp<8>>(entity);
+        (void)position;
+        (void)velocity;
+        (void)comp1;
+        (void)comp2;
+        (void)comp3;
+        (void)comp4;
+        (void)comp5;
+        (void)comp6;
+        (void)comp7;
+        (void)comp8;
+    }
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, IterateTenComponentsPersistent10MHalf) {
+    entt::DefaultRegistry registry;
+    registry.prepare<Position, Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>();
+
+    std::cout << "Iterating over 10000000 entities, ten components, persistent view, half of the entities have all the components" << std::endl;
+
+    for (uint64_t i = 0; i < 10000000L; i++) {
+        auto entity = registry.create<Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>();
+        if(i % 2) { registry.assign<Position>(entity); }
+    }
+
+    Timer timer;
+
+    auto view = registry.persistent<Position, Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>();
+
+    for(auto entity: view) {
+        auto &position = view.get<Position>(entity);
+        auto &velocity = view.get<Velocity>(entity);
+        auto &comp1 = view.get<Comp<1>>(entity);
+        auto &comp2 = view.get<Comp<2>>(entity);
+        auto &comp3 = view.get<Comp<3>>(entity);
+        auto &comp4 = view.get<Comp<4>>(entity);
+        auto &comp5 = view.get<Comp<5>>(entity);
+        auto &comp6 = view.get<Comp<6>>(entity);
+        auto &comp7 = view.get<Comp<7>>(entity);
+        auto &comp8 = view.get<Comp<8>>(entity);
+        (void)position;
+        (void)velocity;
+        (void)comp1;
+        (void)comp2;
+        (void)comp3;
+        (void)comp4;
+        (void)comp5;
+        (void)comp6;
+        (void)comp7;
+        (void)comp8;
+    }
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, IterateTenComponentsPersistent10MOne) {
+    entt::DefaultRegistry registry;
+    registry.prepare<Position, Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>();
+
+    std::cout << "Iterating over 10000000 entities, ten components, persistent view, only one entity has all the components" << std::endl;
+
+    for (uint64_t i = 0; i < 10000000L; i++) {
+        auto entity = registry.create<Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>();
+        if(i == 5000000L) { registry.assign<Position>(entity); }
+    }
+
+    Timer timer;
+
+    auto view = registry.persistent<Position, Velocity, Comp<1>, Comp<2>, Comp<3>, Comp<4>, Comp<5>, Comp<6>, Comp<7>, Comp<8>>();
+
+    for(auto entity: view) {
+        auto &position = view.get<Position>(entity);
+        auto &velocity = view.get<Velocity>(entity);
+        auto &comp1 = view.get<Comp<1>>(entity);
+        auto &comp2 = view.get<Comp<2>>(entity);
+        auto &comp3 = view.get<Comp<3>>(entity);
+        auto &comp4 = view.get<Comp<4>>(entity);
+        auto &comp5 = view.get<Comp<5>>(entity);
+        auto &comp6 = view.get<Comp<6>>(entity);
+        auto &comp7 = view.get<Comp<7>>(entity);
+        auto &comp8 = view.get<Comp<8>>(entity);
+        (void)position;
+        (void)velocity;
+        (void)comp1;
+        (void)comp2;
+        (void)comp3;
+        (void)comp4;
+        (void)comp5;
+        (void)comp6;
+        (void)comp7;
+        (void)comp8;
+    }
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, SortSingle) {
+    entt::DefaultRegistry registry;
+    std::vector<entt::DefaultRegistry::entity_type> entities{};
+
+    std::cout << "Sort 150000 entities, one component" << std::endl;
+
+    for (uint64_t i = 0; i < 150000L; i++) {
+        auto entity = registry.create();
+        entities.push_back(entity);
+        registry.assign<Position>(entity, i, i);
+    }
+
+    Timer timer;
+
+    registry.sort<Position>([&registry](const auto &lhs, const auto &rhs) {
+        return lhs.x < rhs.x && lhs.y < rhs.y;
+    });
+
+    timer.elapsed();
+}
+
+TEST(DefaultRegistry, SortMulti) {
+    entt::DefaultRegistry registry;
+    std::vector<entt::DefaultRegistry::entity_type> entities{};
+
+    std::cout << "Sort 150000 entities, two components" << std::endl;
+
+    for (uint64_t i = 0; i < 150000L; i++) {
+        auto entity = registry.create();
+        entities.push_back(entity);
+        registry.assign<Position>(entity, i, i);
+        registry.assign<Velocity>(entity, i, i);
+    }
+
+    registry.sort<Position>([&registry](const auto &lhs, const auto &rhs) {
+        return lhs.x < rhs.x && lhs.y < rhs.y;
+    });
+
+    Timer timer;
+
+    registry.sort<Velocity, Position>();
+
+    timer.elapsed();
+}

test/entt/entity/registry.cpp

@@ -0,0 +1,197 @@
+#include <functional>
+#include <gtest/gtest.h>
+#include <entt/entity/registry.hpp>
+
+TEST(DefaultRegistry, Functionalities) {
+    entt::DefaultRegistry registry;
+
+    ASSERT_EQ(registry.size(), entt::DefaultRegistry::size_type{0});
+    ASSERT_TRUE(registry.empty());
+
+    ASSERT_EQ(registry.capacity(), entt::DefaultRegistry::size_type{0});
+    ASSERT_EQ(registry.size<int>(), entt::DefaultRegistry::size_type{0});
+    ASSERT_EQ(registry.size<char>(), entt::DefaultRegistry::size_type{0});
+    ASSERT_TRUE(registry.empty<int>());
+    ASSERT_TRUE(registry.empty<char>());
+
+    auto e1 = registry.create();
+    auto e2 = registry.create<int, char>();
+
+    ASSERT_EQ(registry.capacity(), entt::DefaultRegistry::size_type{2});
+    ASSERT_EQ(registry.size<int>(), entt::DefaultRegistry::size_type{1});
+    ASSERT_EQ(registry.size<char>(), entt::DefaultRegistry::size_type{1});
+    ASSERT_FALSE(registry.empty<int>());
+    ASSERT_FALSE(registry.empty<char>());
+
+    ASSERT_NE(e1, e2);
+
+    ASSERT_FALSE(registry.has<int>(e1));
+    ASSERT_TRUE(registry.has<int>(e2));
+    ASSERT_FALSE(registry.has<char>(e1));
+    ASSERT_TRUE(registry.has<char>(e2));
+    ASSERT_FALSE((registry.has<int, char>(e1)));
+    ASSERT_TRUE((registry.has<int, char>(e2)));
+
+    ASSERT_EQ(registry.assign<int>(e1, 42), 42);
+    ASSERT_EQ(registry.assign<char>(e1, 'c'), 'c');
+    ASSERT_NO_THROW(registry.remove<int>(e2));
+    ASSERT_NO_THROW(registry.remove<char>(e2));
+
+    ASSERT_TRUE(registry.has<int>(e1));
+    ASSERT_FALSE(registry.has<int>(e2));
+    ASSERT_TRUE(registry.has<char>(e1));
+    ASSERT_FALSE(registry.has<char>(e2));
+    ASSERT_TRUE((registry.has<int, char>(e1)));
+    ASSERT_FALSE((registry.has<int, char>(e2)));
+
+    auto e3 = registry.create();
+
+    registry.accomodate<int>(e3, registry.get<int>(e1));
+    registry.accomodate<char>(e3, registry.get<char>(e1));
+
+    ASSERT_TRUE(registry.has<int>(e3));
+    ASSERT_TRUE(registry.has<char>(e3));
+    ASSERT_EQ(registry.get<int>(e1), 42);
+    ASSERT_EQ(registry.get<char>(e1), 'c');
+    ASSERT_EQ(registry.get<int>(e1), registry.get<int>(e3));
+    ASSERT_EQ(registry.get<char>(e1), registry.get<char>(e3));
+    ASSERT_NE(&registry.get<int>(e1), &registry.get<int>(e3));
+    ASSERT_NE(&registry.get<char>(e1), &registry.get<char>(e3));
+
+    ASSERT_NO_THROW(registry.replace<int>(e1, 0));
+    ASSERT_EQ(registry.get<int>(e1), 0);
+
+    ASSERT_NO_THROW(registry.accomodate<int>(e1, 1));
+    ASSERT_NO_THROW(registry.accomodate<int>(e2, 1));
+    ASSERT_EQ(static_cast<const entt::DefaultRegistry &>(registry).get<int>(e1), 1);
+    ASSERT_EQ(static_cast<const entt::DefaultRegistry &>(registry).get<int>(e2), 1);
+
+    ASSERT_EQ(registry.size(), entt::DefaultRegistry::size_type{3});
+    ASSERT_FALSE(registry.empty());
+
+    ASSERT_EQ(registry.version(e3), entt::DefaultRegistry::version_type{0});
+    ASSERT_EQ(registry.current(e3), entt::DefaultRegistry::version_type{0});
+    ASSERT_EQ(registry.capacity(), entt::DefaultRegistry::size_type{3});
+    ASSERT_NO_THROW(registry.destroy(e3));
+    ASSERT_EQ(registry.capacity(), entt::DefaultRegistry::size_type{3});
+    ASSERT_EQ(registry.version(e3), entt::DefaultRegistry::version_type{0});
+    ASSERT_EQ(registry.current(e3), entt::DefaultRegistry::version_type{1});
+
+    ASSERT_TRUE(registry.valid(e1));
+    ASSERT_TRUE(registry.valid(e2));
+    ASSERT_FALSE(registry.valid(e3));
+
+    ASSERT_EQ(registry.size(), entt::DefaultRegistry::size_type{2});
+    ASSERT_FALSE(registry.empty());
+
+    ASSERT_NO_THROW(registry.reset());
+
+    ASSERT_EQ(registry.size(), entt::DefaultRegistry::size_type{0});
+    ASSERT_TRUE(registry.empty());
+
+    registry.create<int, char>();
+
+    ASSERT_EQ(registry.size<int>(), entt::DefaultRegistry::size_type{1});
+    ASSERT_EQ(registry.size<char>(), entt::DefaultRegistry::size_type{1});
+    ASSERT_FALSE(registry.empty<int>());
+    ASSERT_FALSE(registry.empty<char>());
+
+    ASSERT_NO_THROW(registry.reset<int>());
+
+    ASSERT_EQ(registry.size<int>(), entt::DefaultRegistry::size_type{0});
+    ASSERT_EQ(registry.size<char>(), entt::DefaultRegistry::size_type{1});
+    ASSERT_TRUE(registry.empty<int>());
+    ASSERT_FALSE(registry.empty<char>());
+
+    ASSERT_NO_THROW(registry.reset());
+
+    ASSERT_EQ(registry.size<int>(), entt::DefaultRegistry::size_type{0});
+    ASSERT_EQ(registry.size<char>(), entt::DefaultRegistry::size_type{0});
+    ASSERT_TRUE(registry.empty<int>());
+    ASSERT_TRUE(registry.empty<char>());
+
+    e1 = registry.create<int>();
+    e2 = registry.create();
+
+    ASSERT_NO_THROW(registry.reset<int>(e1));
+    ASSERT_NO_THROW(registry.reset<int>(e2));
+
+    ASSERT_EQ(registry.size<int>(), entt::DefaultRegistry::size_type{0});
+    ASSERT_EQ(registry.size<char>(), entt::DefaultRegistry::size_type{0});
+    ASSERT_TRUE(registry.empty<int>());
+}
+
+TEST(DefaultRegistry, CreateDestroyEntities) {
+    entt::DefaultRegistry registry;
+
+    auto pre = registry.create<double>();
+    registry.destroy(pre);
+    auto post = registry.create<double>();
+
+    ASSERT_FALSE(registry.valid(pre));
+    ASSERT_TRUE(registry.valid(post));
+    ASSERT_NE(registry.version(pre), registry.version(post));
+    ASSERT_EQ(registry.current(pre), registry.current(post));
+}
+
+TEST(DefaultRegistry, SortSingle) {
+    entt::DefaultRegistry registry;
+
+    auto e1 = registry.create();
+    auto e2 = registry.create();
+    auto e3 = registry.create();
+
+    auto val = 0;
+
+    registry.assign<int>(e1, val++);
+    registry.assign<int>(e2, val++);
+    registry.assign<int>(e3, val++);
+
+    for(auto entity: registry.view<int>()) {
+        ASSERT_EQ(registry.get<int>(entity), --val);
+    }
+
+    registry.sort<int>(std::less<int>{});
+
+    for(auto entity: registry.view<int>()) {
+        ASSERT_EQ(registry.get<int>(entity), val++);
+    }
+}
+
+TEST(DefaultRegistry, SortMulti) {
+    entt::DefaultRegistry registry;
+
+    auto e1 = registry.create();
+    auto e2 = registry.create();
+    auto e3 = registry.create();
+
+    auto uval = 0u;
+    auto ival = 0;
+
+    registry.assign<unsigned int>(e1, uval++);
+    registry.assign<unsigned int>(e2, uval++);
+    registry.assign<unsigned int>(e3, uval++);
+
+    registry.assign<int>(e1, ival++);
+    registry.assign<int>(e2, ival++);
+    registry.assign<int>(e3, ival++);
+
+    for(auto entity: registry.view<unsigned int>()) {
+        ASSERT_EQ(registry.get<unsigned int>(entity), --uval);
+    }
+
+    for(auto entity: registry.view<int>()) {
+        ASSERT_EQ(registry.get<int>(entity), --ival);
+    }
+
+    registry.sort<unsigned int>(std::less<unsigned int>{});
+    registry.sort<int, unsigned int>();
+
+    for(auto entity: registry.view<unsigned int>()) {
+        ASSERT_EQ(registry.get<unsigned int>(entity), uval++);
+    }
+
+    for(auto entity: registry.view<int>()) {
+        ASSERT_EQ(registry.get<int>(entity), ival++);
+    }
+}

test/entt/entity/sparse_set.cpp

@@ -0,0 +1,362 @@
+#include <gtest/gtest.h>
+#include <entt/entity/sparse_set.hpp>
+
+TEST(SparseSetNoType, Functionalities) {
+    entt::SparseSet<unsigned int> set;
+
+    ASSERT_TRUE(set.empty());
+    ASSERT_EQ(set.size(), 0u);
+    ASSERT_EQ(set.begin(), set.end());
+    ASSERT_FALSE(set.has(0));
+    ASSERT_FALSE(set.has(42));
+
+    ASSERT_EQ(set.construct(42), 0u);
+
+    ASSERT_FALSE(set.empty());
+    ASSERT_EQ(set.size(), 1u);
+    ASSERT_NE(set.begin(), set.end());
+    ASSERT_FALSE(set.has(0));
+    ASSERT_TRUE(set.has(42));
+    ASSERT_EQ(set.get(42), 0u);
+
+    set.destroy(42);
+
+    ASSERT_TRUE(set.empty());
+    ASSERT_EQ(set.size(), 0u);
+    ASSERT_EQ(set.begin(), set.end());
+    ASSERT_FALSE(set.has(0));
+    ASSERT_FALSE(set.has(42));
+
+    ASSERT_EQ(set.construct(42), 0u);
+
+    set.reset();
+
+    ASSERT_TRUE(set.empty());
+    ASSERT_EQ(set.size(), 0u);
+    ASSERT_EQ(set.begin(), set.end());
+    ASSERT_FALSE(set.has(0));
+    ASSERT_FALSE(set.has(42));
+
+    (void)entt::SparseSet<unsigned int>{std::move(set)};
+    entt::SparseSet<unsigned int> other;
+    other = std::move(set);
+}
+
+TEST(SparseSetNoType, DataBeginEnd) {
+    entt::SparseSet<unsigned int> set;
+
+    ASSERT_EQ(set.construct(3), 0u);
+    ASSERT_EQ(set.construct(12), 1u);
+    ASSERT_EQ(set.construct(42), 2u);
+
+    ASSERT_EQ(*(set.data() + 0u), 3u);
+    ASSERT_EQ(*(set.data() + 1u), 12u);
+    ASSERT_EQ(*(set.data() + 2u), 42u);
+
+    auto begin = set.begin();
+    auto end = set.end();
+
+    ASSERT_EQ(*(begin++), 42u);
+    ASSERT_EQ(*(begin++), 12u);
+    ASSERT_EQ(*(begin++), 3u);
+    ASSERT_EQ(begin, end);
+}
+
+TEST(SparseSetWithType, Functionalities) {
+    entt::SparseSet<unsigned int, int> set;
+
+    ASSERT_TRUE(set.empty());
+    ASSERT_EQ(set.size(), 0u);
+    ASSERT_EQ(set.begin(), set.end());
+    ASSERT_FALSE(set.has(0));
+    ASSERT_FALSE(set.has(42));
+
+    ASSERT_EQ(set.construct(42, 3), 3);
+
+    ASSERT_FALSE(set.empty());
+    ASSERT_EQ(set.size(), 1u);
+    ASSERT_NE(set.begin(), set.end());
+    ASSERT_FALSE(set.has(0));
+    ASSERT_TRUE(set.has(42));
+    ASSERT_EQ(set.get(42), 3);
+
+    set.destroy(42);
+
+    ASSERT_TRUE(set.empty());
+    ASSERT_EQ(set.size(), 0u);
+    ASSERT_EQ(set.begin(), set.end());
+    ASSERT_FALSE(set.has(0));
+    ASSERT_FALSE(set.has(42));
+
+    ASSERT_EQ(set.construct(42, 12), 12);
+
+    set.reset();
+
+    ASSERT_TRUE(set.empty());
+    ASSERT_EQ(set.size(), 0u);
+    ASSERT_EQ(set.begin(), set.end());
+    ASSERT_FALSE(set.has(0));
+    ASSERT_FALSE(set.has(42));
+
+    (void)entt::SparseSet<unsigned int>{std::move(set)};
+    entt::SparseSet<unsigned int> other;
+    other = std::move(set);
+}
+
+TEST(SparseSetWithType, RawBeginEnd) {
+    entt::SparseSet<unsigned int, int> set;
+
+    ASSERT_EQ(set.construct(3, 3), 3);
+    ASSERT_EQ(set.construct(12, 6), 6);
+    ASSERT_EQ(set.construct(42, 9), 9);
+
+    ASSERT_EQ(*(set.raw() + 0u), 3);
+    ASSERT_EQ(*(set.raw() + 1u), 6);
+    ASSERT_EQ(*(set.raw() + 2u), 9);
+
+    auto begin = set.begin();
+    auto end = set.end();
+
+    ASSERT_EQ(set.get(*(begin++)), 9);
+    ASSERT_EQ(set.get(*(begin++)), 6);
+    ASSERT_EQ(set.get(*(begin++)), 3);
+    ASSERT_EQ(begin, end);
+}
+
+TEST(SparseSetWithType, SortOrdered) {
+    entt::SparseSet<unsigned int, int> set;
+
+    ASSERT_EQ(set.construct(12, 12), 12);
+    ASSERT_EQ(set.construct(42, 9), 9);
+    ASSERT_EQ(set.construct(7, 6), 6);
+    ASSERT_EQ(set.construct(3, 3), 3);
+    ASSERT_EQ(set.construct(9, 1), 1);
+
+    set.sort([&set](auto lhs, auto rhs) {
+        return set.get(lhs) < set.get(rhs);
+    });
+
+    ASSERT_EQ(*(set.raw() + 0u), 12);
+    ASSERT_EQ(*(set.raw() + 1u), 9);
+    ASSERT_EQ(*(set.raw() + 2u), 6);
+    ASSERT_EQ(*(set.raw() + 3u), 3);
+    ASSERT_EQ(*(set.raw() + 4u), 1);
+
+    auto begin = set.begin();
+    auto end = set.end();
+
+    ASSERT_EQ(set.get(*(begin++)), 1);
+    ASSERT_EQ(set.get(*(begin++)), 3);
+    ASSERT_EQ(set.get(*(begin++)), 6);
+    ASSERT_EQ(set.get(*(begin++)), 9);
+    ASSERT_EQ(set.get(*(begin++)), 12);
+    ASSERT_EQ(begin, end);
+}
+
+TEST(SparseSetWithType, SortReverse) {
+    entt::SparseSet<unsigned int, int> set;
+
+    ASSERT_EQ(set.construct(12, 1), 1);
+    ASSERT_EQ(set.construct(42, 3), 3);
+    ASSERT_EQ(set.construct(7, 6), 6);
+    ASSERT_EQ(set.construct(3, 9), 9);
+    ASSERT_EQ(set.construct(9, 12), 12);
+
+    set.sort([&set](auto lhs, auto rhs) {
+        return set.get(lhs) < set.get(rhs);
+    });
+
+    ASSERT_EQ(*(set.raw() + 0u), 12);
+    ASSERT_EQ(*(set.raw() + 1u), 9);
+    ASSERT_EQ(*(set.raw() + 2u), 6);
+    ASSERT_EQ(*(set.raw() + 3u), 3);
+    ASSERT_EQ(*(set.raw() + 4u), 1);
+
+    auto begin = set.begin();
+    auto end = set.end();
+
+    ASSERT_EQ(set.get(*(begin++)), 1);
+    ASSERT_EQ(set.get(*(begin++)), 3);
+    ASSERT_EQ(set.get(*(begin++)), 6);
+    ASSERT_EQ(set.get(*(begin++)), 9);
+    ASSERT_EQ(set.get(*(begin++)), 12);
+    ASSERT_EQ(begin, end);
+}
+
+TEST(SparseSetWithType, SortUnordered) {
+    entt::SparseSet<unsigned int, int> set;
+
+    ASSERT_EQ(set.construct(12, 6), 6);
+    ASSERT_EQ(set.construct(42, 3), 3);
+    ASSERT_EQ(set.construct(7, 1), 1);
+    ASSERT_EQ(set.construct(3, 9), 9);
+    ASSERT_EQ(set.construct(9, 12), 12);
+
+    set.sort([&set](auto lhs, auto rhs) {
+        return set.get(lhs) < set.get(rhs);
+    });
+
+    ASSERT_EQ(*(set.raw() + 0u), 12);
+    ASSERT_EQ(*(set.raw() + 1u), 9);
+    ASSERT_EQ(*(set.raw() + 2u), 6);
+    ASSERT_EQ(*(set.raw() + 3u), 3);
+    ASSERT_EQ(*(set.raw() + 4u), 1);
+
+    auto begin = set.begin();
+    auto end = set.end();
+
+    ASSERT_EQ(set.get(*(begin++)), 1);
+    ASSERT_EQ(set.get(*(begin++)), 3);
+    ASSERT_EQ(set.get(*(begin++)), 6);
+    ASSERT_EQ(set.get(*(begin++)), 9);
+    ASSERT_EQ(set.get(*(begin++)), 12);
+    ASSERT_EQ(begin, end);
+}
+
+TEST(SparseSetWithType, RespectDisjoint) {
+    entt::SparseSet<unsigned int, int> lhs;
+    entt::SparseSet<unsigned int, int> rhs;
+    const auto &clhs = lhs;
+
+    ASSERT_EQ(lhs.construct(3, 3), 3);
+    ASSERT_EQ(lhs.construct(12, 6), 6);
+    ASSERT_EQ(lhs.construct(42, 9), 9);
+
+    lhs.respect(rhs);
+
+    ASSERT_EQ(*(clhs.raw() + 0u), 3);
+    ASSERT_EQ(*(clhs.raw() + 1u), 6);
+    ASSERT_EQ(*(clhs.raw() + 2u), 9);
+
+    auto begin = clhs.begin();
+    auto end = clhs.end();
+
+    ASSERT_EQ(clhs.get(*(begin++)), 9);
+    ASSERT_EQ(clhs.get(*(begin++)), 6);
+    ASSERT_EQ(clhs.get(*(begin++)), 3);
+    ASSERT_EQ(begin, end);
+}
+
+TEST(SparseSetWithType, RespectOverlap) {
+    entt::SparseSet<unsigned int, int> lhs;
+    entt::SparseSet<unsigned int, int> rhs;
+    const auto &clhs = lhs;
+
+    ASSERT_EQ(lhs.construct(3, 3), 3);
+    ASSERT_EQ(lhs.construct(12, 6), 6);
+    ASSERT_EQ(lhs.construct(42, 9), 9);
+    ASSERT_EQ(rhs.construct(12, 6), 6);
+
+    lhs.respect(rhs);
+
+    ASSERT_EQ(*(clhs.raw() + 0u), 3);
+    ASSERT_EQ(*(clhs.raw() + 1u), 9);
+    ASSERT_EQ(*(clhs.raw() + 2u), 6);
+
+    auto begin = clhs.begin();
+    auto end = clhs.end();
+
+    ASSERT_EQ(clhs.get(*(begin++)), 6);
+    ASSERT_EQ(clhs.get(*(begin++)), 9);
+    ASSERT_EQ(clhs.get(*(begin++)), 3);
+    ASSERT_EQ(begin, end);
+}
+
+TEST(SparseSetWithType, RespectOrdered) {
+    entt::SparseSet<unsigned int, int> lhs;
+    entt::SparseSet<unsigned int, int> rhs;
+
+    ASSERT_EQ(lhs.construct(1, 0), 0);
+    ASSERT_EQ(lhs.construct(2, 0), 0);
+    ASSERT_EQ(lhs.construct(3, 0), 0);
+    ASSERT_EQ(lhs.construct(4, 0), 0);
+    ASSERT_EQ(lhs.construct(5, 0), 0);
+
+    ASSERT_EQ(rhs.construct(6, 0), 0);
+    ASSERT_EQ(rhs.construct(1, 0), 0);
+    ASSERT_EQ(rhs.construct(2, 0), 0);
+    ASSERT_EQ(rhs.construct(3, 0), 0);
+    ASSERT_EQ(rhs.construct(4, 0), 0);
+    ASSERT_EQ(rhs.construct(5, 0), 0);
+
+    rhs.respect(lhs);
+
+    ASSERT_EQ(*(lhs.data() + 0u), 1u);
+    ASSERT_EQ(*(lhs.data() + 1u), 2u);
+    ASSERT_EQ(*(lhs.data() + 2u), 3u);
+    ASSERT_EQ(*(lhs.data() + 3u), 4u);
+    ASSERT_EQ(*(lhs.data() + 4u), 5u);
+
+    ASSERT_EQ(*(rhs.data() + 0u), 6u);
+    ASSERT_EQ(*(rhs.data() + 1u), 1u);
+    ASSERT_EQ(*(rhs.data() + 2u), 2u);
+    ASSERT_EQ(*(rhs.data() + 3u), 3u);
+    ASSERT_EQ(*(rhs.data() + 4u), 4u);
+    ASSERT_EQ(*(rhs.data() + 5u), 5u);
+}
+
+TEST(SparseSetWithType, RespectReverse) {
+    entt::SparseSet<unsigned int, int> lhs;
+    entt::SparseSet<unsigned int, int> rhs;
+
+    ASSERT_EQ(lhs.construct(1, 0), 0);
+    ASSERT_EQ(lhs.construct(2, 0), 0);
+    ASSERT_EQ(lhs.construct(3, 0), 0);
+    ASSERT_EQ(lhs.construct(4, 0), 0);
+    ASSERT_EQ(lhs.construct(5, 0), 0);
+
+    ASSERT_EQ(rhs.construct(5, 0), 0);
+    ASSERT_EQ(rhs.construct(4, 0), 0);
+    ASSERT_EQ(rhs.construct(3, 0), 0);
+    ASSERT_EQ(rhs.construct(2, 0), 0);
+    ASSERT_EQ(rhs.construct(1, 0), 0);
+    ASSERT_EQ(rhs.construct(6, 0), 0);
+
+    rhs.respect(lhs);
+
+    ASSERT_EQ(*(lhs.data() + 0u), 1u);
+    ASSERT_EQ(*(lhs.data() + 1u), 2u);
+    ASSERT_EQ(*(lhs.data() + 2u), 3u);
+    ASSERT_EQ(*(lhs.data() + 3u), 4u);
+    ASSERT_EQ(*(lhs.data() + 4u), 5u);
+
+    ASSERT_EQ(*(rhs.data() + 0u), 6u);
+    ASSERT_EQ(*(rhs.data() + 1u), 1u);
+    ASSERT_EQ(*(rhs.data() + 2u), 2u);
+    ASSERT_EQ(*(rhs.data() + 3u), 3u);
+    ASSERT_EQ(*(rhs.data() + 4u), 4u);
+    ASSERT_EQ(*(rhs.data() + 5u), 5u);
+}
+
+TEST(SparseSetWithType, RespectUnordered) {
+    entt::SparseSet<unsigned int, int> lhs;
+    entt::SparseSet<unsigned int, int> rhs;
+
+    ASSERT_EQ(lhs.construct(1, 0), 0);
+    ASSERT_EQ(lhs.construct(2, 0), 0);
+    ASSERT_EQ(lhs.construct(3, 0), 0);
+    ASSERT_EQ(lhs.construct(4, 0), 0);
+    ASSERT_EQ(lhs.construct(5, 0), 0);
+
+    ASSERT_EQ(rhs.construct(3, 0), 0);
+    ASSERT_EQ(rhs.construct(2, 0), 0);
+    ASSERT_EQ(rhs.construct(6, 0), 0);
+    ASSERT_EQ(rhs.construct(1, 0), 0);
+    ASSERT_EQ(rhs.construct(4, 0), 0);
+    ASSERT_EQ(rhs.construct(5, 0), 0);
+
+    rhs.respect(lhs);
+
+    ASSERT_EQ(*(lhs.data() + 0u), 1u);
+    ASSERT_EQ(*(lhs.data() + 1u), 2u);
+    ASSERT_EQ(*(lhs.data() + 2u), 3u);
+    ASSERT_EQ(*(lhs.data() + 3u), 4u);
+    ASSERT_EQ(*(lhs.data() + 4u), 5u);
+
+    ASSERT_EQ(*(rhs.data() + 0u), 6u);
+    ASSERT_EQ(*(rhs.data() + 1u), 1u);
+    ASSERT_EQ(*(rhs.data() + 2u), 2u);
+    ASSERT_EQ(*(rhs.data() + 3u), 3u);
+    ASSERT_EQ(*(rhs.data() + 4u), 4u);
+    ASSERT_EQ(*(rhs.data() + 5u), 5u);
+}

test/entt/entity/view.cpp

@@ -0,0 +1,228 @@
+#include <gtest/gtest.h>
+#include <entt/entity/registry.hpp>
+#include <entt/entity/view.hpp>
+
+TEST(View, SingleComponent) {
+    entt::DefaultRegistry registry;
+
+    auto e1 = registry.create();
+    auto e2 = registry.create<int, char>();
+
+    ASSERT_NO_THROW(registry.view<char>().begin()++);
+    ASSERT_NO_THROW(++registry.view<char>().begin());
+
+    auto view = registry.view<char>();
+
+    ASSERT_NE(view.begin(), view.end());
+    ASSERT_EQ(view.size(), typename decltype(view)::size_type{1});
+
+    registry.assign<char>(e1);
+
+    ASSERT_EQ(view.size(), typename decltype(view)::size_type{2});
+
+    view.get(e1) = '1';
+    view.get(e2) = '2';
+
+    for(auto entity: view) {
+        const auto &cview = static_cast<const decltype(view) &>(view);
+        ASSERT_TRUE(cview.get(entity) == '1' || cview.get(entity) == '2');
+    }
+
+    ASSERT_EQ(*(view.data() + 0), e2);
+    ASSERT_EQ(*(view.data() + 1), e1);
+
+    ASSERT_EQ(*(view.raw() + 0), '2');
+    ASSERT_EQ(*(static_cast<const decltype(view) &>(view).raw() + 1), '1');
+
+    registry.remove<char>(e1);
+    registry.remove<char>(e2);
+
+    ASSERT_EQ(view.begin(), view.end());
+}
+
+TEST(View, SingleComponentEmpty) {
+    entt::DefaultRegistry registry;
+
+    registry.create<char, double>();
+    registry.create<char>();
+
+    auto view = registry.view<int>();
+
+    ASSERT_EQ(view.size(), entt::DefaultRegistry::size_type{0});
+
+    for(auto entity: view) {
+        (void)entity;
+        FAIL();
+    }
+}
+
+TEST(View, MultipleComponent) {
+    entt::DefaultRegistry registry;
+
+    auto e1 = registry.create<char>();
+    auto e2 = registry.create<int, char>();
+
+    ASSERT_NO_THROW((registry.view<int, char>().begin()++));
+    ASSERT_NO_THROW((++registry.view<int, char>().begin()));
+
+    auto view = registry.view<int, char>();
+
+    ASSERT_NE(view.begin(), view.end());
+
+    view.get<char>(e1) = '1';
+    view.get<char>(e2) = '2';
+
+    for(auto entity: view) {
+        const auto &cview = static_cast<const decltype(view) &>(view);
+        ASSERT_TRUE(cview.get<char>(entity) == '2');
+    }
+
+    registry.remove<char>(e1);
+    registry.remove<char>(e2);
+    view.reset();
+
+    ASSERT_EQ(view.begin(), view.end());
+}
+
+TEST(View, MultipleComponentEmpty) {
+    entt::DefaultRegistry registry;
+
+    registry.create<double, int, float>();
+    registry.create<char, float>();
+
+    auto view = registry.view<char, int, float>();
+
+    for(auto entity: view) {
+        (void)entity;
+        FAIL();
+    }
+}
+
+TEST(PersistentView, MultipleComponentPrepare) {
+    entt::DefaultRegistry registry;
+    registry.prepare<int, char>();
+
+    auto e1 = registry.create<char>();
+    auto e2 = registry.create<int, char>();
+
+    ASSERT_NO_THROW((registry.persistent<int, char>().begin()++));
+    ASSERT_NO_THROW((++registry.persistent<int, char>().begin()));
+
+    auto view = registry.persistent<int, char>();
+
+    ASSERT_NE(view.begin(), view.end());
+    ASSERT_EQ(view.size(), typename decltype(view)::size_type{1});
+
+    registry.assign<int>(e1);
+
+    ASSERT_EQ(view.size(), typename decltype(view)::size_type{2});
+
+    registry.remove<int>(e1);
+
+    ASSERT_EQ(view.size(), typename decltype(view)::size_type{1});
+
+    view.get<char>(e1) = '1';
+    view.get<char>(e2) = '2';
+
+    for(auto entity: view) {
+        const auto &cview = static_cast<const decltype(view) &>(view);
+        ASSERT_TRUE(cview.get<char>(entity) == '2');
+    }
+
+    ASSERT_EQ(*(view.data() + 0), e2);
+
+    registry.remove<char>(e1);
+    registry.remove<char>(e2);
+
+    ASSERT_EQ(view.begin(), view.end());
+}
+
+TEST(PersistentView, MultipleComponentNoPrepare) {
+    entt::DefaultRegistry registry;
+
+    auto e1 = registry.create<char>();
+    auto e2 = registry.create<int, char>();
+
+    ASSERT_NO_THROW((registry.persistent<int, char>().begin()++));
+    ASSERT_NO_THROW((++registry.persistent<int, char>().begin()));
+
+    auto view = registry.persistent<int, char>();
+
+    ASSERT_NE(view.begin(), view.end());
+    ASSERT_EQ(view.size(), typename decltype(view)::size_type{1});
+
+    registry.assign<int>(e1);
+
+    ASSERT_EQ(view.size(), typename decltype(view)::size_type{2});
+
+    registry.remove<int>(e1);
+
+    ASSERT_EQ(view.size(), typename decltype(view)::size_type{1});
+
+    view.get<char>(e1) = '1';
+    view.get<char>(e2) = '2';
+
+    for(auto entity: view) {
+        const auto &cview = static_cast<const decltype(view) &>(view);
+        ASSERT_TRUE(cview.get<char>(entity) == '2');
+    }
+
+    ASSERT_EQ(*(view.data() + 0), e2);
+
+    registry.remove<char>(e1);
+    registry.remove<char>(e2);
+
+    ASSERT_EQ(view.begin(), view.end());
+}
+
+TEST(PersistentView, MultipleComponentEmpty) {
+    entt::DefaultRegistry registry;
+
+    registry.create<double, int, float>();
+    registry.create<char, float>();
+
+    for(auto entity: registry.persistent<char, int, float>()) {
+        (void)entity;
+        FAIL();
+    }
+
+    for(auto entity: registry.persistent<double, char, int, float>()) {
+        (void)entity;
+        FAIL();
+    }
+}
+
+TEST(PersistentView, Sort) {
+    entt::DefaultRegistry registry;
+    registry.prepare<int, unsigned int>();
+
+    auto e1 = registry.create();
+    auto e2 = registry.create();
+    auto e3 = registry.create();
+
+    auto uval = 0u;
+    auto ival = 0;
+
+    registry.assign<unsigned int>(e1, uval++);
+    registry.assign<unsigned int>(e2, uval++);
+    registry.assign<unsigned int>(e3, uval++);
+
+    registry.assign<int>(e1, ival++);
+    registry.assign<int>(e2, ival++);
+    registry.assign<int>(e3, ival++);
+
+    auto view = registry.persistent<int, unsigned int>();
+
+    for(auto entity: view) {
+        ASSERT_EQ(view.get<unsigned int>(entity), --uval);
+        ASSERT_EQ(view.get<int>(entity), --ival);
+    }
+
+    registry.sort<unsigned int>(std::less<unsigned int>{});
+    view.sort<unsigned int>();
+
+    for(auto entity: view) {
+        ASSERT_EQ(view.get<unsigned int>(entity), uval++);
+        ASSERT_EQ(view.get<int>(entity), ival++);
+    }
+}

test/entt/signal/sigh.cpp

@@ -0,0 +1,197 @@
+#include <utility>
+#include <vector>
+#include <gtest/gtest.h>
+#include <entt/signal/sigh.hpp>
+
+TEST(SigH, Lifetime) {
+    using signal = entt::SigH<void(void)>;
+
+    ASSERT_NO_THROW(signal{});
+
+    signal src{}, other{};
+
+    ASSERT_NO_THROW(signal{src});
+    ASSERT_NO_THROW(signal{std::move(other)});
+    ASSERT_NO_THROW(src = other);
+    ASSERT_NO_THROW(src = std::move(other));
+
+    ASSERT_NO_THROW(delete new signal{});
+}
+
+TEST(SigH, Comparison) {
+    struct S {
+        void f() {}
+        void g() {}
+    };
+
+    entt::SigH<void()> sig1;
+    entt::SigH<void()> sig2;
+
+    S s1;
+    S s2;
+
+    sig1.connect<S, &S::f>(&s1);
+    sig2.connect<S, &S::f>(&s2);
+
+    ASSERT_FALSE(sig1 == sig2);
+    ASSERT_TRUE(sig1 != sig2);
+
+    sig1.disconnect<S, &S::f>(&s1);
+    sig2.disconnect<S, &S::f>(&s2);
+
+    sig1.connect<S, &S::f>(&s1);
+    sig2.connect<S, &S::g>(&s1);
+
+    ASSERT_FALSE(sig1 == sig2);
+    ASSERT_TRUE(sig1 != sig2);
+
+    sig1.disconnect<S, &S::f>(&s1);
+    sig2.disconnect<S, &S::g>(&s1);
+
+    ASSERT_TRUE(sig1 == sig2);
+    ASSERT_FALSE(sig1 != sig2);
+
+    sig1.connect<S, &S::f>(&s1);
+    sig1.connect<S, &S::g>(&s1);
+    sig2.connect<S, &S::f>(&s1);
+    sig2.connect<S, &S::g>(&s1);
+
+    ASSERT_TRUE(sig1 == sig2);
+
+    sig1.disconnect<S, &S::f>(&s1);
+    sig1.disconnect<S, &S::g>(&s1);
+    sig2.disconnect<S, &S::f>(&s1);
+    sig2.disconnect<S, &S::g>(&s1);
+
+    sig1.connect<S, &S::f>(&s1);
+    sig1.connect<S, &S::g>(&s1);
+    sig2.connect<S, &S::g>(&s1);
+    sig2.connect<S, &S::f>(&s1);
+
+    ASSERT_FALSE(sig1 == sig2);
+}
+
+struct S {
+    static void f(int &v) { v = 42; }
+};
+
+TEST(SigH, Functions) {
+    entt::SigH<void(int &)> sigh;
+    int v = 0;
+
+    sigh.connect<&S::f>();
+    sigh.publish(v);
+
+    ASSERT_FALSE(sigh.empty());
+    ASSERT_EQ((entt::SigH<bool(int)>::size_type)1, sigh.size());
+    ASSERT_EQ(42, v);
+
+    v = 0;
+    sigh.disconnect<&S::f>();
+    sigh.publish(v);
+
+    ASSERT_TRUE(sigh.empty());
+    ASSERT_EQ((entt::SigH<bool(int)>::size_type)0, sigh.size());
+    ASSERT_EQ(0, v);
+}
+
+TEST(SigH, Members) {
+    struct S {
+        bool f(int) { b = !b; return true; }
+        bool g(int) { return b; }
+        bool b{false};
+    };
+
+    S s;
+    S *ptr = &s;
+    entt::SigH<bool(int)> sigh;
+
+    sigh.connect<S, &S::f>(ptr);
+    sigh.publish(42);
+
+    ASSERT_TRUE(s.b);
+    ASSERT_FALSE(sigh.empty());
+    ASSERT_EQ((entt::SigH<bool(int)>::size_type)1, sigh.size());
+
+    sigh.disconnect<S, &S::f>(ptr);
+    sigh.publish(42);
+
+    ASSERT_TRUE(s.b);
+    ASSERT_TRUE(sigh.empty());
+    ASSERT_EQ((entt::SigH<bool(int)>::size_type)0, sigh.size());
+
+    sigh.connect<S, &S::f>(ptr);
+    sigh.connect<S, &S::g>(ptr);
+
+    ASSERT_FALSE(sigh.empty());
+    ASSERT_EQ((entt::SigH<bool(int)>::size_type)2, sigh.size());
+
+    sigh.disconnect(ptr);
+
+    ASSERT_TRUE(sigh.empty());
+    ASSERT_EQ((entt::SigH<bool(int)>::size_type)0, sigh.size());
+}
+
+template<typename Ret>
+struct TestCollectAll {
+    std::vector<Ret> vec{};
+    static int f() { return 42; }
+    static int g() { return 42; }
+    bool operator()(Ret r) noexcept {
+        vec.push_back(r);
+        return true;
+    }
+};
+
+template<>
+struct TestCollectAll<void> {
+    std::vector<int> vec{};
+    static void h() {}
+    bool operator()() noexcept {
+        return true;
+    }
+};
+
+template<typename Ret>
+struct TestCollectFirst {
+    std::vector<Ret> vec{};
+    static int f() { return 42; }
+    bool operator()(Ret r) noexcept {
+        vec.push_back(r);
+        return false;
+    }
+};
+
+TEST(SigH, Collector) {
+    entt::SigH<void(), TestCollectAll<void>> sigh_void;
+
+    sigh_void.connect<&TestCollectAll<void>::h>();
+    auto collector_void = sigh_void.collect();
+
+    ASSERT_FALSE(sigh_void.empty());
+    ASSERT_TRUE(collector_void.vec.empty());
+
+    entt::SigH<int(), TestCollectAll<int>> sigh_all;
+
+    sigh_all.connect<&TestCollectAll<int>::f>();
+    sigh_all.connect<&TestCollectAll<int>::f>();
+    sigh_all.connect<&TestCollectAll<int>::g>();
+    auto collector_all = sigh_all.collect();
+
+    ASSERT_FALSE(sigh_all.empty());
+    ASSERT_FALSE(collector_all.vec.empty());
+    ASSERT_EQ((std::vector<int>::size_type)2, collector_all.vec.size());
+    ASSERT_EQ(42, collector_all.vec[0]);
+    ASSERT_EQ(42, collector_all.vec[1]);
+
+    entt::SigH<int(), TestCollectFirst<int>> sigh_first;
+
+    sigh_first.connect<&TestCollectFirst<int>::f>();
+    sigh_first.connect<&TestCollectFirst<int>::f>();
+    auto collector_first = sigh_first.collect();
+
+    ASSERT_FALSE(sigh_first.empty());
+    ASSERT_FALSE(collector_first.vec.empty());
+    ASSERT_EQ((std::vector<int>::size_type)1, collector_first.vec.size());
+    ASSERT_EQ(42, collector_first.vec[0]);
+}

test/odr.cpp

@@ -0,0 +1 @@
+#include <entt/entt.hpp>

test/registry.cpp

@@ -1,233 +0,0 @@
-#include <gtest/gtest.h>
-#include <registry.hpp>
-
-TEST(DefaultRegistry, Functionalities) {
-    using registry_type = entt::DefaultRegistry<int, char>;
-
-    registry_type registry;
-
-    ASSERT_EQ(registry.size(), registry_type::size_type{0});
-    ASSERT_EQ(registry.capacity(), registry_type::size_type{0});
-    ASSERT_TRUE(registry.empty());
-
-    ASSERT_TRUE(registry.empty<int>());
-    ASSERT_TRUE(registry.empty<char>());
-
-    registry_type::entity_type e1 = registry.create();
-    registry_type::entity_type e2 = registry.create<int, char>();
-
-    ASSERT_FALSE(registry.empty<int>());
-    ASSERT_FALSE(registry.empty<char>());
-
-    ASSERT_NE(e1, e2);
-
-    ASSERT_FALSE(registry.has<int>(e1));
-    ASSERT_TRUE(registry.has<int>(e2));
-    ASSERT_FALSE(registry.has<char>(e1));
-    ASSERT_TRUE(registry.has<char>(e2));
-    ASSERT_TRUE((registry.has<int, char>(e2)));
-    ASSERT_FALSE((registry.has<int, char>(e1)));
-
-    ASSERT_EQ(registry.assign<int>(e1, 42), 42);
-    ASSERT_EQ(registry.assign<char>(e1, 'c'), 'c');
-    ASSERT_NO_THROW(registry.remove<int>(e2));
-    ASSERT_NO_THROW(registry.remove<char>(e2));
-
-    ASSERT_TRUE(registry.has<int>(e1));
-    ASSERT_FALSE(registry.has<int>(e2));
-    ASSERT_TRUE(registry.has<char>(e1));
-    ASSERT_FALSE(registry.has<char>(e2));
-    ASSERT_TRUE((registry.has<int, char>(e1)));
-    ASSERT_FALSE((registry.has<int, char>(e2)));
-
-    registry_type::entity_type e3 = registry.clone(e1);
-
-    ASSERT_TRUE(registry.has<int>(e3));
-    ASSERT_TRUE(registry.has<char>(e3));
-    ASSERT_EQ(registry.get<int>(e1), 42);
-    ASSERT_EQ(registry.get<char>(e1), 'c');
-    ASSERT_EQ(registry.get<int>(e1), registry.get<int>(e3));
-    ASSERT_EQ(registry.get<char>(e1), registry.get<char>(e3));
-    ASSERT_NE(&registry.get<int>(e1), &registry.get<int>(e3));
-    ASSERT_NE(&registry.get<char>(e1), &registry.get<char>(e3));
-
-    ASSERT_NO_THROW(registry.copy(e2, e1));
-    ASSERT_TRUE(registry.has<int>(e2));
-    ASSERT_TRUE(registry.has<char>(e2));
-    ASSERT_EQ(registry.get<int>(e1), 42);
-    ASSERT_EQ(registry.get<char>(e1), 'c');
-    ASSERT_EQ(registry.get<int>(e1), registry.get<int>(e2));
-    ASSERT_EQ(registry.get<char>(e1), registry.get<char>(e2));
-    ASSERT_NE(&registry.get<int>(e1), &registry.get<int>(e2));
-    ASSERT_NE(&registry.get<char>(e1), &registry.get<char>(e2));
-
-    ASSERT_NO_THROW(registry.replace<int>(e1, 0));
-    ASSERT_EQ(registry.get<int>(e1), 0);
-    ASSERT_NO_THROW(registry.copy<int>(e2, e1));
-    ASSERT_EQ(registry.get<int>(e2), 0);
-    ASSERT_NE(&registry.get<int>(e1), &registry.get<int>(e2));
-
-    ASSERT_NO_THROW(registry.remove<int>(e2));
-    ASSERT_NO_THROW(registry.accomodate<int>(e1, 1));
-    ASSERT_NO_THROW(registry.accomodate<int>(e2, 1));
-    ASSERT_EQ(static_cast<const registry_type &>(registry).get<int>(e1), 1);
-    ASSERT_EQ(static_cast<const registry_type &>(registry).get<int>(e2), 1);
-
-    ASSERT_EQ(registry.size(), registry_type::size_type{3});
-    ASSERT_EQ(registry.capacity(), registry_type::size_type{3});
-    ASSERT_FALSE(registry.empty());
-
-    ASSERT_NO_THROW(registry.destroy(e3));
-
-    ASSERT_TRUE(registry.valid(e1));
-    ASSERT_TRUE(registry.valid(e2));
-    ASSERT_FALSE(registry.valid(e3));
-
-    ASSERT_EQ(registry.size(), registry_type::size_type{2});
-    ASSERT_EQ(registry.capacity(), registry_type::size_type{3});
-    ASSERT_FALSE(registry.empty());
-
-    ASSERT_NO_THROW(registry.reset());
-
-    ASSERT_EQ(registry.size(), registry_type::size_type{0});
-    ASSERT_EQ(registry.capacity(), registry_type::size_type{0});
-    ASSERT_TRUE(registry.empty());
-
-    registry.create<int, char>();
-
-    ASSERT_FALSE(registry.empty<int>());
-    ASSERT_FALSE(registry.empty<char>());
-
-    ASSERT_NO_THROW(registry.reset<int>());
-
-    ASSERT_TRUE(registry.empty<int>());
-    ASSERT_FALSE(registry.empty<char>());
-
-    ASSERT_NO_THROW(registry.reset());
-
-    ASSERT_TRUE(registry.empty<int>());
-    ASSERT_TRUE(registry.empty<char>());
-
-    e1 = registry.create<int>();
-    e2 = registry.create();
-
-    ASSERT_NO_THROW(registry.reset<int>(e1));
-    ASSERT_NO_THROW(registry.reset<int>(e2));
-    ASSERT_TRUE(registry.empty<int>());
-}
-
-TEST(DefaultRegistry, Copy) {
-    using registry_type = entt::DefaultRegistry<int, char, double>;
-
-    registry_type registry;
-
-    registry_type::entity_type e1 = registry.create<int, char>();
-    registry_type::entity_type e2 = registry.create<int, double>();
-
-    ASSERT_TRUE(registry.has<int>(e1));
-    ASSERT_TRUE(registry.has<char>(e1));
-    ASSERT_FALSE(registry.has<double>(e1));
-
-    ASSERT_TRUE(registry.has<int>(e2));
-    ASSERT_FALSE(registry.has<char>(e2));
-    ASSERT_TRUE(registry.has<double>(e2));
-
-    ASSERT_NO_THROW(registry.copy(e2, e1));
-
-    ASSERT_TRUE(registry.has<int>(e1));
-    ASSERT_TRUE(registry.has<char>(e1));
-    ASSERT_FALSE(registry.has<double>(e1));
-
-    ASSERT_TRUE(registry.has<int>(e2));
-    ASSERT_TRUE(registry.has<char>(e2));
-    ASSERT_FALSE(registry.has<double>(e2));
-
-    ASSERT_FALSE(registry.empty<int>());
-    ASSERT_FALSE(registry.empty<char>());
-    ASSERT_TRUE(registry.empty<double>());
-
-    registry.reset();
-}
-
-TEST(DefaultRegistry, ViewSingleComponent) {
-    using registry_type = entt::DefaultRegistry<int, char>;
-
-    registry_type registry;
-
-    registry_type::entity_type e1 = registry.create();
-    registry_type::entity_type e2 = registry.create<int, char>();
-
-    ASSERT_NO_THROW(registry.view<char>().begin()++);
-    ASSERT_NO_THROW(++registry.view<char>().begin());
-
-    auto view = registry.view<char>();
-
-    ASSERT_NE(view.begin(), view.end());
-    ASSERT_EQ(view.size(), typename registry_type::view_type<char>::size_type{1});
-
-    registry.assign<char>(e1);
-
-    ASSERT_EQ(view.size(), typename registry_type::view_type<char>::size_type{2});
-
-    registry.remove<char>(e1);
-    registry.remove<char>(e2);
-
-    ASSERT_EQ(view.begin(), view.end());
-    ASSERT_NO_THROW(registry.reset());
-}
-
-TEST(DefaultRegistry, ViewMultipleComponent) {
-    using registry_type = entt::DefaultRegistry<int, char>;
-
-    registry_type registry;
-
-    registry_type::entity_type e1 = registry.create<char>();
-    registry_type::entity_type e2 = registry.create<int, char>();
-
-    ASSERT_NO_THROW((registry.view<int, char>().begin()++));
-    ASSERT_NO_THROW((++registry.view<int, char>().begin()));
-
-    auto view = registry.view<int, char>();
-
-    ASSERT_NE(view.begin(), view.end());
-
-    registry.remove<char>(e1);
-    registry.remove<char>(e2);
-    view.reset();
-
-    ASSERT_EQ(view.begin(), view.end());
-    ASSERT_NO_THROW(registry.reset());
-}
-
-TEST(DefaultRegistry, EmptyViewSingleComponent) {
-    using registry_type = entt::DefaultRegistry<char, int, double>;
-
-    registry_type registry;
-
-    registry.create<char, double>();
-    registry.create<char>();
-
-    auto view = registry.view<int>();
-
-    ASSERT_EQ(view.size(), registry_type::size_type{0});
-
-    registry.reset();
-}
-
-TEST(DefaultRegistry, EmptyViewMultipleComponent) {
-    using registry_type = entt::DefaultRegistry<char, int, float, double>;
-
-    registry_type registry;
-
-    registry.create<double, int, float>();
-    registry.create<char, float>();
-
-    auto view = registry.view<char, int, float>();
-
-    for(auto entity: view) {
-        (void)entity;
-        FAIL();
-    }
-
-    registry.reset();
-}