EnTT v2 (#14)

EnTT v2

CMakeLists.txt

@@ -16,7 +16,7 @@ endif()
 # Project configuration
 #
 
-project(entt VERSION 1.1.0)
+project(entt VERSION 2.0.0)
 
 if(NOT CMAKE_BUILD_TYPE)
     set(CMAKE_BUILD_TYPE Debug)
@@ -33,7 +33,7 @@ message("* Copyright (c) 2017 ${PROJECT_AUTHOR} <${PROJECT_AUTHOR_EMAIL}>")
 message("*")
 
 #
-# Compile stuff
+# Compiler stuff
 #
 
 set(CMAKE_CXX_STANDARD 14)
@@ -41,7 +41,7 @@ set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
 if(NOT MSVC)
     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 "${CMAKE_CXX_FLAGS} -pedantic -Wall")
     set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -DRELEASE")
     set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -O0 -g -DDEBUG")
 
@@ -65,15 +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)
@@ -89,3 +85,13 @@ if(BUILD_TESTING)
     enable_testing()
     add_subdirectory(test)
 endif()
+
+#
+# Documentation
+#
+
+find_package(Doxygen 1.8)
+
+if(DOXYGEN_FOUND)
+    add_subdirectory(docs)
+endif()

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 @@
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docs/extra.dox

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

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 +1,746 @@
+#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);
+        entities[entt] = entt | (version << traits_type::version_shift);
+        available.push_back(entity);
+
+        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

@@ -1,443 +0,0 @@
-#ifndef ENTT_REGISTRY_HPP
-#define ENTT_REGISTRY_HPP
-
-
-#include <tuple>
-#include <vector>
-#include <bitset>
-#include <utility>
-#include <cstddef>
-#include <cassert>
-#include <type_traits>
-#include "sparse_set.hpp"
-#include "ident.hpp"
-
-
-namespace entt {
-
-
-template<typename, std::size_t...>
-class View;
-
-
-template<typename Pool, std::size_t Ident, std::size_t... Other>
-class View<Pool, Ident, Other...> final {
-    using pool_type = Pool;
-    using mask_type = std::bitset<std::tuple_size<Pool>::value + 1>;
-    using underlying_iterator_type = typename std::tuple_element_t<Ident, Pool>::iterator_type;
-
-    class ViewIterator;
-
-public:
-    using iterator_type = ViewIterator;
-    using entity_type = typename std::tuple_element_t<Ident, Pool>::index_type;
-    using size_type = typename std::tuple_element_t<Ident, Pool>::size_type;
-
-private:
-    class ViewIterator {
-        inline bool valid() const noexcept {
-            return ((mask[*begin] & bitmask) == bitmask);
-        }
-
-    public:
-        using value_type = entity_type;
-
-        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<std::size_t Idx>
-    void prefer(size_type &size) noexcept {
-        auto &&cpool = std::get<Idx>(*pool);
-        auto sz = cpool.size();
-
-        if(sz < size) {
-            from = cpool.begin();
-            to = cpool.end();
-            size = sz;
-        }
-    }
-
-public:
-    explicit View(const pool_type *pool, const mask_type *mask) noexcept
-        : from{std::get<Ident>(*pool).begin()},
-          to{std::get<Ident>(*pool).end()},
-          pool{pool},
-          mask{mask}
-    {
-        using accumulator_type = int[];
-        size_type size = std::get<Ident>(*pool).size();
-        bitmask.set(Ident);
-        accumulator_type types = { 0, (bitmask.set(Other), 0)... };
-        accumulator_type pref = { 0, (prefer<Other>(size), 0)... };
-        (void)types, (void)pref;
-    }
-
-    iterator_type begin() const noexcept {
-        return ViewIterator{from, to, bitmask, mask};
-    }
-
-    iterator_type end() const noexcept {
-        return ViewIterator{to, to, bitmask, mask};
-    }
-
-    void reset() noexcept {
-        using accumulator_type = int[];
-        auto &&cpool = std::get<Ident>(*pool);
-        from = cpool.begin();
-        to = cpool.end();
-        size_type size = cpool.size();
-        accumulator_type accumulator = { 0, (prefer<Other>(size), 0)... };
-        (void)accumulator;
-    }
-
-private:
-    underlying_iterator_type from;
-    underlying_iterator_type to;
-    const pool_type *pool;
-    const mask_type *mask;
-    mask_type bitmask;
-};
-
-
-template<typename Pool, std::size_t Ident>
-class View<Pool, Ident> final {
-    using pool_type = std::tuple_element_t<Ident, Pool>;
-
-public:
-    using iterator_type = typename pool_type::iterator_type;
-    using entity_type = typename pool_type::index_type;
-    using size_type = typename pool_type::size_type;
-    using raw_type = typename pool_type::type;
-
-    explicit View(const Pool *pool) noexcept
-        : pool{&std::get<Ident>(*pool)}
-    {}
-
-    raw_type * raw() noexcept {
-        return pool->raw();
-    }
-
-    const raw_type * raw() const noexcept {
-        return pool->raw();
-    }
-
-    const entity_type * data() const noexcept {
-        return pool->data();
-    }
-
-    size_type size() const noexcept {
-        return pool->size();
-    }
-
-    iterator_type begin() const noexcept {
-        return pool->begin();
-    }
-
-    iterator_type end() const noexcept {
-        return pool->end();
-    }
-
-private:
-    const pool_type *pool;
-};
-
-
-template<typename Entity, typename... Component>
-class Registry {
-    using pool_type = std::tuple<SparseSet<Entity, Component>...>;
-    using mask_type = std::bitset<sizeof...(Component)+1>;
-
-    static constexpr auto validity_bit = sizeof...(Component);
-
-    // variable templates are fine as well, but for the fact that MSVC goes crazy
-    template<typename Comp>
-    struct identifier {
-        static constexpr auto value = ident<Component...>.template get<Comp>();
-    };
-
-public:
-    using entity_type = Entity;
-    using size_type = typename std::vector<mask_type>::size_type;
-
-    template<typename... Comp>
-    using view_type = View<pool_type, identifier<Comp>::value...>;
-
-private:
-    template<typename Comp>
-    void clone(entity_type to, entity_type from) {
-        if(entities[from].test(identifier<Comp>::value)) {
-            assign<Comp>(to, std::get<identifier<Comp>::value>(pool).get(from));
-        }
-    }
-
-    template<typename Comp>
-    void sync(entity_type to, entity_type from) {
-        bool src = entities[from].test(identifier<Comp>::value);
-        bool dst = entities[to].test(identifier<Comp>::value);
-
-        if(src && dst) {
-            copy<Comp>(to, from);
-        } else if(src) {
-            clone<Comp>(to, from);
-        } else if(dst) {
-            remove<Comp>(to);
-        }
-    }
-
-public:
-    explicit Registry() = default;
-    ~Registry() = default;
-
-    Registry(const Registry &) = delete;
-    Registry(Registry &&) = delete;
-
-    Registry & operator=(const Registry &) = delete;
-    Registry & operator=(Registry &&) = delete;
-
-    template<typename Comp>
-    size_type size() const noexcept {
-        return std::get<identifier<Comp>::value>(pool).size();
-    }
-
-    size_type size() const noexcept {
-        return entities.size() - available.size();
-    }
-
-    template<typename Comp>
-    size_type capacity() const noexcept {
-        return std::get<identifier<Comp>::value>(pool).capacity();
-    }
-
-    size_type capacity() const noexcept {
-        return entities.size();
-    }
-
-    template<typename Comp>
-    bool empty() const noexcept {
-        return std::get<identifier<Comp>::value>(pool).empty();
-    }
-
-    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<Component>(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(identifier<Comp>::value);
-        return std::get<identifier<Comp>::value>(pool).construct(entity, args...);
-    }
-
-    template<typename Comp>
-    void remove(entity_type entity) {
-        assert(valid(entity));
-        entities[entity].reset(identifier<Comp>::value);
-        std::get<identifier<Comp>::value>(pool).destroy(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(identifier<Comp>::value))... };
-        (void)accumulator;
-        return all;
-    }
-
-    template<typename Comp>
-    const Comp & get(entity_type entity) const noexcept {
-        assert(valid(entity));
-        return std::get<identifier<Comp>::value>(pool).get(entity);
-    }
-
-    template<typename Comp>
-    Comp & get(entity_type entity) noexcept {
-        assert(valid(entity));
-        return std::get<identifier<Comp>::value>(pool).get(entity);
-    }
-
-    template<typename Comp, typename... Args>
-    Comp & replace(entity_type entity, Args... args) {
-        assert(valid(entity));
-        return (std::get<identifier<Comp>::value>(pool).get(entity) = Comp{args...});
-    }
-
-    template<typename Comp, typename... Args>
-    Comp & accomodate(entity_type entity, Args... args) {
-        assert(valid(entity));
-
-        return (entities[entity].test(identifier<Comp>::value)
-                ? 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<Component>(to, from), 0)... };
-        (void)accumulator;
-        return to;
-    }
-
-    template<typename Comp>
-    Comp & copy(entity_type to, entity_type from) {
-        assert(valid(to));
-        assert(valid(from));
-        auto &&cpool = std::get<identifier<Comp>::value>(pool);
-        return (cpool.get(to) = cpool.get(from));
-    }
-
-    void copy(entity_type to, entity_type from) {
-        assert(valid(to));
-        assert(valid(from));
-        using accumulator_type = int[];
-        accumulator_type accumulator = { 0, (sync<Component>(to, from), 0)... };
-        (void)accumulator;
-    }
-
-    template<typename Comp>
-    void swap(entity_type lhs, entity_type rhs) {
-        assert(valid(lhs));
-        assert(valid(rhs));
-        std::get<identifier<Comp>::value>(pool).swap(lhs, rhs);
-    }
-
-    template<typename Comp, typename Compare>
-    void sort(Compare compare) {
-        std::get<identifier<Comp>::value>(pool).sort(std::move(compare));
-    }
-
-    template<typename To, typename From>
-    void sort() {
-        auto &&to = std::get<identifier<To>::value>(pool);
-        auto &&from = std::get<identifier<From>::value>(pool);
-        to.respect(from);
-    }
-
-    template<typename Comp>
-    void reset(entity_type entity) {
-        assert(valid(entity));
-
-        if(entities[entity].test(identifier<Comp>::value)) {
-            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(identifier<Comp>::value)) {
-                remove<Comp>(entity);
-            }
-        }
-    }
-
-    void reset() {
-        using accumulator_type = int[];
-        accumulator_type acc = { 0, (std::get<identifier<Component>::value>(pool).reset(), 0)... };
-        entities.clear();
-        available.clear();
-        (void)acc;
-    }
-
-    template<typename... Comp>
-    // view_type<Comp...> is fine as well, but for the fact that MSVC dislikes it
-    std::enable_if_t<(sizeof...(Comp) == 1), View<pool_type, identifier<Comp>::value...>>
-    view() noexcept { return view_type<Comp...>{&pool}; }
-
-    template<typename... Comp>
-    // view_type<Comp...> is fine as well, but for the fact that MSVC dislikes it
-    std::enable_if_t<(sizeof...(Comp) > 1), View<pool_type, identifier<Comp>::value...>>
-    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... Component>
-using DefaultRegistry = Registry<std::uint32_t, Component...>;
-
-
-}
-
-
-#endif // ENTT_REGISTRY_HPP

src/sparse_set.hpp

@@ -1,277 +0,0 @@
-#ifndef ENTT_COMPONENT_POOL_HPP
-#define ENTT_COMPONENT_POOL_HPP
-
-
-#include <algorithm>
-#include <utility>
-#include <numeric>
-#include <vector>
-#include <cstddef>
-#include <cassert>
-
-
-namespace entt {
-
-
-template<typename...>
-class SparseSet;
-
-
-template<typename Index>
-class SparseSet<Index> {
-    struct SparseSetIterator;
-
-public:
-    using index_type = Index;
-    using pos_type = index_type;
-    using size_type = std::size_t;
-    using iterator_type = SparseSetIterator;
-
-private:
-    struct SparseSetIterator {
-        using value_type = index_type;
-
-        SparseSetIterator(const std::vector<index_type> *direct, size_type pos)
-            : direct{direct}, pos{pos}
-        {}
-
-        SparseSetIterator & operator++() noexcept {
-            return --pos, *this;
-        }
-
-        SparseSetIterator operator++(int) noexcept {
-            SparseSetIterator orig = *this;
-            return ++(*this), orig;
-        }
-
-        bool operator==(const SparseSetIterator &other) const noexcept {
-            return other.pos == pos && other.direct == direct;
-        }
-
-        bool operator!=(const SparseSetIterator &other) const noexcept {
-            return !(*this == other);
-        }
-
-        value_type operator*() const noexcept {
-            return (*direct)[pos-1];
-        }
-
-    private:
-        const std::vector<index_type> *direct;
-        size_type pos;
-    };
-
-    inline bool valid(Index idx) const noexcept {
-        return idx < reverse.size() && reverse[idx] < direct.size() && direct[reverse[idx]] == idx;
-    }
-
-public:
-    explicit SparseSet() = default;
-
-    SparseSet(const SparseSet &) = delete;
-    SparseSet(SparseSet &&) = default;
-
-    ~SparseSet() noexcept {
-        assert(empty());
-    }
-
-    SparseSet & operator=(const SparseSet &) = delete;
-    SparseSet & operator=(SparseSet &&) = default;
-
-    size_type size() const noexcept {
-        return direct.size();
-    }
-
-    size_t capacity() const noexcept {
-        return direct.capacity();
-    }
-
-    bool empty() const noexcept {
-        return direct.empty();
-    }
-
-    const index_type * data() const noexcept {
-        return direct.data();
-    }
-
-    iterator_type begin() const noexcept {
-        return SparseSetIterator{&direct, direct.size()};
-    }
-
-    iterator_type end() const noexcept {
-        return SparseSetIterator{&direct, 0};
-    }
-
-    bool has(index_type idx) const noexcept {
-        return valid(idx);
-    }
-
-    pos_type get(index_type idx) const noexcept {
-        assert(valid(idx));
-        return reverse[idx];
-    }
-
-    pos_type construct(index_type idx) {
-        assert(!valid(idx));
-
-        if(!(idx < reverse.size())) {
-            reverse.resize(idx+1);
-        }
-
-        auto pos = pos_type(direct.size());
-        reverse[idx] = pos;
-        direct.emplace_back(idx);
-
-        return pos;
-    }
-
-    pos_type destroy(index_type idx) {
-        assert(valid(idx));
-
-        auto last = direct.size() - 1;
-        auto pos = reverse[idx];
-
-        reverse[direct[last]] = pos;
-        direct[pos] = direct[last];
-        direct.pop_back();
-
-        return pos;
-    }
-
-    void swap(index_type lhs, index_type rhs) {
-        assert(valid(lhs));
-        assert(valid(rhs));
-
-        std::swap(direct[reverse[lhs]], direct[reverse[rhs]]);
-        std::swap(reverse[lhs], reverse[rhs]);
-    }
-
-    void reset() {
-        reverse.clear();
-        direct.clear();
-    }
-
-private:
-    std::vector<pos_type> reverse;
-    std::vector<index_type> direct;
-};
-
-
-template<typename Index, typename Type>
-class SparseSet<Index, Type> final: public SparseSet<Index> {
-    template<typename Compare>
-    void arrange(Compare compare) {
-        const auto *data = SparseSet<Index>::data();
-        const auto size = SparseSet<Index>::size();
-        std::vector<pos_type> copy(size);
-
-        std::iota(copy.begin(), copy.end(), pos_type{});
-        std::sort(copy.begin(), copy.end(), compare);
-
-        for(pos_type i = 0; i < copy.size(); ++i) {
-            const auto target = i;
-            auto curr = i;
-
-            while(copy[curr] != target) {
-                SparseSet<Index>::swap(*(data + copy[curr]), *(data + curr));
-                std::swap(instances[copy[curr]], instances[curr]);
-                std::swap(copy[curr], curr);
-            }
-
-            copy[curr] = curr;
-        }
-    }
-
-public:
-    using type = Type;
-    using index_type = typename SparseSet<Index>::index_type;
-    using pos_type = typename SparseSet<Index>::pos_type;
-    using size_type = typename SparseSet<Index>::size_type;
-    using iterator_type = typename SparseSet<Index>::iterator_type;
-
-    explicit SparseSet() = default;
-
-    SparseSet(const SparseSet &) = delete;
-    SparseSet(SparseSet &&) = default;
-
-    SparseSet & operator=(const SparseSet &) = delete;
-    SparseSet & operator=(SparseSet &&) = default;
-
-    type * raw() noexcept {
-        return instances.data();
-    }
-
-    const type * raw() const noexcept {
-        return instances.data();
-    }
-
-    const type & get(index_type idx) const noexcept {
-        return instances[SparseSet<Index>::get(idx)];
-    }
-
-    type & get(index_type idx) noexcept {
-        return const_cast<type &>(const_cast<const SparseSet *>(this)->get(idx));
-    }
-
-    template<typename... Args>
-    type & construct(index_type idx, Args&&... args) {
-        SparseSet<Index>::construct(idx);
-        instances.push_back({ std::forward<Args>(args)... });
-        return instances.back();
-    }
-
-    void destroy(index_type idx) {
-        auto pos = SparseSet<Index>::destroy(idx);
-        instances[pos] = std::move(instances[SparseSet<Index>::size()]);
-        instances.pop_back();
-    }
-
-    void swap(index_type lhs, index_type rhs) {
-        std::swap(instances[SparseSet<Index>::get(lhs)], instances[SparseSet<Index>::get(rhs)]);
-    }
-
-    template<typename Compare>
-    void sort(Compare compare) {
-        arrange([this, compare = std::move(compare)](auto lhs, auto rhs) {
-            return !compare(instances[lhs], instances[rhs]);
-        });
-    }
-
-    template<typename Idx>
-    void respect(const SparseSet<Idx> &other) {
-        const auto *data = SparseSet<Index>::data();
-
-        arrange([data, &other](auto lhs, auto rhs) {
-            auto eLhs = *(data + lhs);
-            auto eRhs = *(data + rhs);
-
-            bool bLhs = other.has(eLhs);
-            bool bRhs = other.has(eRhs);
-            bool compare = false;
-
-            if(bLhs && bRhs) {
-                compare = other.get(eLhs) < other.get(eRhs);
-            } else if(!bLhs && !bRhs) {
-                compare = eLhs < eRhs;
-            } else {
-                compare = bRhs;
-            }
-
-            return compare;
-        });
-    }
-
-    void reset() {
-        SparseSet<Index>::reset();
-        instances.clear();
-    }
-
-private:
-    std::vector<type> instances;
-};
-
-
-}
-
-
-#endif // ENTT_COMPONENT_POOL_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(${TARGET_ENTT} ident.cpp registry.cpp sparse_set.cpp)
-target_include_directories(${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

@@ -1,410 +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/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

@@ -1,5 +1,5 @@
 #include <gtest/gtest.h>
-#include <ident.hpp>
+#include <entt/core/ident.hpp>
 
 struct A {};
 struct B {};

test/entt/entity/benchmark.cpp

@@ -0,0 +1,687 @@
+#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();
+    registry.reset();
+}
+
+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();
+    registry.reset();
+}
+
+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();
+    registry.reset();
+}
+
+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();
+    registry.reset();
+}
+
+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();
+    registry.reset();
+}
+
+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();
+    registry.reset();
+}
+
+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();
+    registry.reset();
+}
+
+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();
+    registry.reset();
+}
+
+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();
+    registry.reset();
+}
+
+TEST(DefaultRegistry, IterateSingleComponent50M) {
+    entt::DefaultRegistry 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();
+    registry.reset();
+}
+
+TEST(DefaultRegistry, IterateTwoComponents50M) {
+    entt::DefaultRegistry 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();
+    registry.reset();
+}
+
+TEST(DefaultRegistry, IterateTwoComponentsPersistent50M) {
+    entt::DefaultRegistry 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();
+    registry.reset();
+}
+
+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();
+    registry.reset();
+}
+
+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();
+    registry.reset();
+}
+
+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();
+    registry.reset();
+}
+
+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();
+    registry.reset();
+}
+
+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();
+    registry.reset();
+}
+
+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();
+    registry.reset();
+}
+
+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();
+    registry.reset();
+}
+
+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();
+    registry.reset();
+}
+
+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 +1,184 @@
+#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, 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

@@ -1,14 +1,11 @@
 #include <gtest/gtest.h>
-#include <sparse_set.hpp>
+#include <entt/entity/sparse_set.hpp>
 
 TEST(SparseSetNoType, Functionalities) {
-    using SparseSet = entt::SparseSet<unsigned int>;
-
-    SparseSet set;
+    entt::SparseSet<unsigned int> set;
 
     ASSERT_TRUE(set.empty());
     ASSERT_EQ(set.size(), 0u);
-    ASSERT_EQ(set.capacity(), 0u);
     ASSERT_EQ(set.begin(), set.end());
     ASSERT_FALSE(set.has(0));
     ASSERT_FALSE(set.has(42));
@@ -17,17 +14,15 @@ TEST(SparseSetNoType, Functionalities) {
 
     ASSERT_FALSE(set.empty());
     ASSERT_EQ(set.size(), 1u);
-    ASSERT_GE(set.capacity(), 1u);
     ASSERT_NE(set.begin(), set.end());
     ASSERT_FALSE(set.has(0));
     ASSERT_TRUE(set.has(42));
     ASSERT_EQ(set.get(42), 0u);
 
-    ASSERT_EQ(set.destroy(42), 0u);
+    set.destroy(42);
 
     ASSERT_TRUE(set.empty());
     ASSERT_EQ(set.size(), 0u);
-    ASSERT_GE(set.capacity(), 1u);
     ASSERT_EQ(set.begin(), set.end());
     ASSERT_FALSE(set.has(0));
     ASSERT_FALSE(set.has(42));
@@ -38,16 +33,17 @@ TEST(SparseSetNoType, Functionalities) {
 
     ASSERT_TRUE(set.empty());
     ASSERT_EQ(set.size(), 0u);
-    ASSERT_GE(set.capacity(), 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) {
-    using SparseSet = entt::SparseSet<unsigned int>;
-
-    SparseSet set;
+    entt::SparseSet<unsigned int> set;
 
     ASSERT_EQ(set.construct(3), 0u);
     ASSERT_EQ(set.construct(12), 1u);
@@ -64,37 +60,13 @@ TEST(SparseSetNoType, DataBeginEnd) {
     ASSERT_EQ(*(begin++), 12u);
     ASSERT_EQ(*(begin++), 3u);
     ASSERT_EQ(begin, end);
-
-    set.reset();
-}
-
-TEST(SparseSetNoType, Swap) {
-    using SparseSet = entt::SparseSet<unsigned int>;
-
-    SparseSet set;
-
-    ASSERT_EQ(set.construct(3), 0u);
-    ASSERT_EQ(set.construct(12), 1u);
-
-    ASSERT_EQ(*(set.data() + 0u), 3u);
-    ASSERT_EQ(*(set.data() + 1u), 12u);
-
-    set.swap(3, 12);
-
-    ASSERT_EQ(*(set.data() + 0u), 12u);
-    ASSERT_EQ(*(set.data() + 1u), 3u);
-
-    set.reset();
 }
 
 TEST(SparseSetWithType, Functionalities) {
-    using SparseSet = entt::SparseSet<unsigned int, int>;
-
-    SparseSet set;
+    entt::SparseSet<unsigned int, int> set;
 
     ASSERT_TRUE(set.empty());
     ASSERT_EQ(set.size(), 0u);
-    ASSERT_EQ(set.capacity(), 0u);
     ASSERT_EQ(set.begin(), set.end());
     ASSERT_FALSE(set.has(0));
     ASSERT_FALSE(set.has(42));
@@ -103,7 +75,6 @@ TEST(SparseSetWithType, Functionalities) {
 
     ASSERT_FALSE(set.empty());
     ASSERT_EQ(set.size(), 1u);
-    ASSERT_GE(set.capacity(), 1u);
     ASSERT_NE(set.begin(), set.end());
     ASSERT_FALSE(set.has(0));
     ASSERT_TRUE(set.has(42));
@@ -113,7 +84,6 @@ TEST(SparseSetWithType, Functionalities) {
 
     ASSERT_TRUE(set.empty());
     ASSERT_EQ(set.size(), 0u);
-    ASSERT_GE(set.capacity(), 1u);
     ASSERT_EQ(set.begin(), set.end());
     ASSERT_FALSE(set.has(0));
     ASSERT_FALSE(set.has(42));
@@ -124,16 +94,17 @@ TEST(SparseSetWithType, Functionalities) {
 
     ASSERT_TRUE(set.empty());
     ASSERT_EQ(set.size(), 0u);
-    ASSERT_GE(set.capacity(), 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) {
-    using SparseSet = entt::SparseSet<unsigned int, int>;
-
-    SparseSet set;
+    entt::SparseSet<unsigned int, int> set;
 
     ASSERT_EQ(set.construct(3, 3), 3);
     ASSERT_EQ(set.construct(12, 6), 6);
@@ -150,33 +121,10 @@ TEST(SparseSetWithType, RawBeginEnd) {
     ASSERT_EQ(set.get(*(begin++)), 6);
     ASSERT_EQ(set.get(*(begin++)), 3);
     ASSERT_EQ(begin, end);
-
-    set.reset();
-}
-
-TEST(SparseSetWithType, Swap) {
-    using SparseSet = entt::SparseSet<unsigned int, int>;
-
-    SparseSet set;
-
-    ASSERT_EQ(set.construct(3, 3), 3);
-    ASSERT_EQ(set.construct(12, 6), 6);
-
-    ASSERT_EQ(*(set.raw() + 0u), 3);
-    ASSERT_EQ(*(set.raw() + 1u), 6);
-
-    set.swap(3, 12);
-
-    ASSERT_EQ(*(set.raw() + 0u), 6);
-    ASSERT_EQ(*(set.raw() + 1u), 3);
-
-    set.reset();
 }
 
 TEST(SparseSetWithType, SortOrdered) {
-    using SparseSet = entt::SparseSet<unsigned int, int>;
-
-    SparseSet set;
+    entt::SparseSet<unsigned int, int> set;
 
     ASSERT_EQ(set.construct(12, 12), 12);
     ASSERT_EQ(set.construct(42, 9), 9);
@@ -184,8 +132,8 @@ TEST(SparseSetWithType, SortOrdered) {
     ASSERT_EQ(set.construct(3, 3), 3);
     ASSERT_EQ(set.construct(9, 1), 1);
 
-    set.sort([](auto lhs, auto rhs) {
-        return lhs < rhs;
+    set.sort([&set](auto lhs, auto rhs) {
+        return set.get(lhs) < set.get(rhs);
     });
 
     ASSERT_EQ(*(set.raw() + 0u), 12);
@@ -203,14 +151,10 @@ TEST(SparseSetWithType, SortOrdered) {
     ASSERT_EQ(set.get(*(begin++)), 9);
     ASSERT_EQ(set.get(*(begin++)), 12);
     ASSERT_EQ(begin, end);
-
-    set.reset();
 }
 
 TEST(SparseSetWithType, SortReverse) {
-    using SparseSet = entt::SparseSet<unsigned int, int>;
-
-    SparseSet set;
+    entt::SparseSet<unsigned int, int> set;
 
     ASSERT_EQ(set.construct(12, 1), 1);
     ASSERT_EQ(set.construct(42, 3), 3);
@@ -218,8 +162,8 @@ TEST(SparseSetWithType, SortReverse) {
     ASSERT_EQ(set.construct(3, 9), 9);
     ASSERT_EQ(set.construct(9, 12), 12);
 
-    set.sort([](auto lhs, auto rhs) {
-        return lhs < rhs;
+    set.sort([&set](auto lhs, auto rhs) {
+        return set.get(lhs) < set.get(rhs);
     });
 
     ASSERT_EQ(*(set.raw() + 0u), 12);
@@ -237,14 +181,10 @@ TEST(SparseSetWithType, SortReverse) {
     ASSERT_EQ(set.get(*(begin++)), 9);
     ASSERT_EQ(set.get(*(begin++)), 12);
     ASSERT_EQ(begin, end);
-
-    set.reset();
 }
 
 TEST(SparseSetWithType, SortUnordered) {
-    using SparseSet = entt::SparseSet<unsigned int, int>;
-
-    SparseSet set;
+    entt::SparseSet<unsigned int, int> set;
 
     ASSERT_EQ(set.construct(12, 6), 6);
     ASSERT_EQ(set.construct(42, 3), 3);
@@ -252,8 +192,8 @@ TEST(SparseSetWithType, SortUnordered) {
     ASSERT_EQ(set.construct(3, 9), 9);
     ASSERT_EQ(set.construct(9, 12), 12);
 
-    set.sort([](auto lhs, auto rhs) {
-        return lhs < rhs;
+    set.sort([&set](auto lhs, auto rhs) {
+        return set.get(lhs) < set.get(rhs);
     });
 
     ASSERT_EQ(*(set.raw() + 0u), 12);
@@ -271,15 +211,60 @@ TEST(SparseSetWithType, SortUnordered) {
     ASSERT_EQ(set.get(*(begin++)), 9);
     ASSERT_EQ(set.get(*(begin++)), 12);
     ASSERT_EQ(begin, end);
+}
 
-    set.reset();
+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) {
-    using SparseSet = entt::SparseSet<unsigned int, int>;
-
-    SparseSet lhs;
-    SparseSet rhs;
+    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);
@@ -308,16 +293,11 @@ TEST(SparseSetWithType, RespectOrdered) {
     ASSERT_EQ(*(rhs.data() + 3u), 3u);
     ASSERT_EQ(*(rhs.data() + 4u), 4u);
     ASSERT_EQ(*(rhs.data() + 5u), 5u);
-
-    lhs.reset();
-    rhs.reset();
 }
 
 TEST(SparseSetWithType, RespectReverse) {
-    using SparseSet = entt::SparseSet<unsigned int, int>;
-
-    SparseSet lhs;
-    SparseSet rhs;
+    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);
@@ -346,16 +326,11 @@ TEST(SparseSetWithType, RespectReverse) {
     ASSERT_EQ(*(rhs.data() + 3u), 3u);
     ASSERT_EQ(*(rhs.data() + 4u), 4u);
     ASSERT_EQ(*(rhs.data() + 5u), 5u);
-
-    lhs.reset();
-    rhs.reset();
 }
 
 TEST(SparseSetWithType, RespectUnordered) {
-    using SparseSet = entt::SparseSet<unsigned int, int>;
-
-    SparseSet lhs;
-    SparseSet rhs;
+    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);
@@ -384,7 +359,4 @@ TEST(SparseSetWithType, RespectUnordered) {
     ASSERT_EQ(*(rhs.data() + 3u), 3u);
     ASSERT_EQ(*(rhs.data() + 4u), 4u);
     ASSERT_EQ(*(rhs.data() + 5u), 5u);
-
-    lhs.reset();
-    rhs.reset();
 }

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

@@ -1,357 +0,0 @@
-#include <gtest/gtest.h>
-#include <registry.hpp>
-#include <functional>
-
-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_EQ(registry.size<int>(), registry_type::size_type{0});
-    ASSERT_EQ(registry.size<char>(), registry_type::size_type{0});
-    ASSERT_EQ(registry.capacity<int>(), registry_type::size_type{0});
-    ASSERT_EQ(registry.capacity<char>(), registry_type::size_type{0});
-    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_EQ(registry.size<int>(), registry_type::size_type{1});
-    ASSERT_EQ(registry.size<char>(), registry_type::size_type{1});
-    ASSERT_GE(registry.capacity<int>(), registry_type::size_type{1});
-    ASSERT_GE(registry.capacity<char>(), registry_type::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_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_EQ(registry.size<int>(), registry_type::size_type{1});
-    ASSERT_EQ(registry.size<char>(), registry_type::size_type{1});
-    ASSERT_GE(registry.capacity<int>(), registry_type::size_type{1});
-    ASSERT_GE(registry.capacity<char>(), registry_type::size_type{1});
-    ASSERT_FALSE(registry.empty<int>());
-    ASSERT_FALSE(registry.empty<char>());
-
-    ASSERT_NO_THROW(registry.reset<int>());
-
-    ASSERT_EQ(registry.size<int>(), registry_type::size_type{0});
-    ASSERT_EQ(registry.size<char>(), registry_type::size_type{1});
-    ASSERT_GE(registry.capacity<int>(), registry_type::size_type{0});
-    ASSERT_GE(registry.capacity<char>(), registry_type::size_type{1});
-    ASSERT_TRUE(registry.empty<int>());
-    ASSERT_FALSE(registry.empty<char>());
-
-    ASSERT_NO_THROW(registry.reset());
-
-    ASSERT_EQ(registry.size<int>(), registry_type::size_type{0});
-    ASSERT_EQ(registry.size<char>(), registry_type::size_type{0});
-    ASSERT_GE(registry.capacity<int>(), registry_type::size_type{0});
-    ASSERT_GE(registry.capacity<char>(), registry_type::size_type{1});
-    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>(), registry_type::size_type{0});
-    ASSERT_EQ(registry.size<char>(), registry_type::size_type{0});
-    ASSERT_GE(registry.capacity<int>(), registry_type::size_type{0});
-    ASSERT_GE(registry.capacity<char>(), registry_type::size_type{0});
-    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, Swap) {
-    using registry_type = entt::DefaultRegistry<int, char>;
-
-    registry_type registry;
-
-    registry_type::entity_type e1 = registry.create<int, char>();
-    registry_type::entity_type e2 = registry.create<int, char>();
-
-    registry.get<int>(e1) = 0;
-    registry.get<char>(e1) = 'a';
-    registry.get<int>(e2) = 1;
-    registry.get<char>(e2) = 'b';
-
-    registry.swap<int>(e1, e2);
-
-    ASSERT_EQ(registry.get<int>(e1), 1);
-    ASSERT_EQ(registry.get<char>(e1), 'a');
-    ASSERT_EQ(registry.get<int>(e2), 0);
-    ASSERT_EQ(registry.get<char>(e2), 'b');
-
-    registry.reset();
-}
-
-TEST(DefaultRegistry, SortSingle) {
-    using registry_type = entt::DefaultRegistry<int>;
-
-    registry_type registry;
-
-    registry_type::entity_type e1 = registry.create();
-    registry_type::entity_type e2 = registry.create();
-    registry_type::entity_type 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++);
-    }
-
-    registry.reset();
-}
-
-TEST(DefaultRegistry, SortMulti) {
-    using registry_type = entt::DefaultRegistry<int, unsigned int>;
-
-    registry_type registry;
-
-    registry_type::entity_type e1 = registry.create();
-    registry_type::entity_type e2 = registry.create();
-    registry_type::entity_type 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++);
-    }
-
-    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 decltype(view)::size_type{1});
-
-    registry.assign<char>(e1);
-
-    ASSERT_EQ(view.size(), typename decltype(view)::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, ViewSingleComponentEmpty) {
-    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});
-
-    for(auto entity: view) {
-        (void)entity;
-        FAIL();
-    }
-
-    registry.reset();
-}
-
-TEST(DefaultRegistry, ViewMultipleComponentEmpty) {
-    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();
-}