Implement entt::Prototype (#74)

first draft - to be reviewed

src/entt/entity/prototype.hpp

@@ -0,0 +1,226 @@
+#ifndef ENTT_ENTITY_PROTOTYPE_HPP
+#define ENTT_ENTITY_PROTOTYPE_HPP
+
+#include "registry.hpp"
+
+namespace entt {
+
+/**
+ * @brief A prototype entity for creating new entities
+ *
+ * Prototype provides a similar interface to the registry except that Prototype
+ * stores a single entity. This entity is not apart of the registry so it is not
+ * seen by views. The Prototype can be used to accommodate components to an
+ * entity on the registry.
+ *
+ * Note that components stored in the Prototype must have copy constructors to
+ * initialize an entity.
+ *
+ * @tparam Entity A valid entity type (see entt_traits for more details).
+ */
+template <typename Entity>
+class Prototype {
+public:
+    using entity_t = Entity;
+    using registry_t = entt::Registry<Entity>;
+    using family_t = entt::Family<struct PrototypeFamily>;
+
+private:
+    struct StorageBase {
+        virtual ~StorageBase() = default;
+        virtual void accommodate(registry_t &, entity_t) const ENTT_NOEXCEPT = 0;
+    };
+    
+    template <typename Component>
+    struct Storage : StorageBase {
+        void accommodate(registry_t &reg, const entity_t entity) const ENTT_NOEXCEPT override {
+            reg.template accommodate<Component>(entity, comp);
+        }
+        
+        Component comp;
+    };
+
+public:
+    Prototype() = default;
+    Prototype(Prototype &&) = default;
+    Prototype &operator=(Prototype &&) = default;
+
+    /**
+     * @brief Checks if there exists at least one component assigned
+     *
+     * @return True if no components are assigned
+     */
+    bool empty() const ENTT_NOEXCEPT {
+        return std::all_of(comps.cbegin(), comps.cend(), [] (auto comp) {
+            return comp == nullptr;
+        });
+    }
+
+    /**
+     * @brief Accommodate copies of the components to the given entity
+     */
+    void operator()(registry_t &reg, const entity_t entity) const ENTT_NOEXCEPT {
+        for (const std::unique_ptr<StorageBase> &component : comps) {
+            if (component) {
+                component->accommodate(reg, entity);
+            }
+        }
+    }
+    /**
+     * @brief Create an new entity assign copies of the components to it
+     *
+     * @return Newly created entity
+     */
+    entity_t operator()(registry_t &reg) const ENTT_NOEXCEPT {
+        const entity_t entity = reg.create();
+        (*this)(reg, entity);
+        return entity;
+    }
+
+    /**
+     * @brief Returns the numeric identifier of a type of component at runtime
+     *
+     * The component doesn't need to be assigned to the prototype for this
+     * function to return a valid ID. The IDs are not synced with the registry.
+     *
+     * @tparam Component Type of component to query.
+     * @return Runtime numeric identifier of the given type of component
+     */
+    template <typename Component>
+    size_t type() const ENTT_NOEXCEPT {
+        return family_t::template type<Component>();
+    }
+
+    /**
+     * @brief Assigns the given component to the prototype
+     *
+     * @warning
+     * An assertion will abort the execution at runtime in debug mode in case
+     * the prototype already owns the given component
+     *
+     * @tparam Component Type of component to create
+     * @tparam Args Types of arguments to use to construct the component.
+     * @param args Parameters to use to initialize the component.
+     * @return A reference to the newly created component.
+     */
+    template <typename Component, typename... Args>
+    Component &assign(Args &&... args) {
+        assert(!has<Component>());
+        auto component = std::make_unique<Storage<Component>>();
+        component->comp = Component {std::forward<Args>(args)...};
+        const size_t index = type<Component>();
+        while (comps.size() <= index) {
+            comps.emplace_back();
+        }
+        Component &comp = component->comp;
+        comps[index] = std::move(component);
+        return comp;
+    }
+    
+    /**
+     * @brief Removes the given component from the prototype
+     *
+     * @warning
+     * An assertion will abort the execution at runtime in debug mode in case
+     * the prototype doesn't own the given component
+     *
+     * @tparam Component Type of component to remove
+     */
+    template <typename Component>
+    void remove() ENTT_NOEXCEPT {
+        assert(has<Component>());
+        comps[type<Component>()] = nullptr;
+    }
+    
+    /**
+     * @brief Checks if the prototype has all the given components
+     *
+     * @tparam Components Components that the prototype must own
+     * @return True if the prototype owns all of the components, false otherwise.
+     */
+    template <typename... Components>
+    bool has() const ENTT_NOEXCEPT {
+        bool all = true;
+        [[maybe_unused]]
+        bool acc[] = {(all = all && type<Components>() < comps.size() && comps[type<Components>()] != nullptr)...};
+        return all;
+    }
+    
+    /**
+     * @brief Returns a const reference to the given component
+     *
+     * @warning
+     * An assertion will abort the execution at runtime in debug mode in case
+     * the prototype doesn't own the given component
+     *
+     * @tparam Component Type of component to get
+     * @return A reference to the component
+     */
+    template <typename Component>
+    const Component &get() const ENTT_NOEXCEPT {
+        assert(has<Component>());
+        return static_cast<Storage<Component> *>(comps[type<Component>()].get())->comp;
+    }
+    
+    /**
+     * @brief Returns a reference to the given component
+     *
+     * @warning
+     * An assertion will abort the execution at runtime in debug mode in case
+     * the prototype doesn't own the given component
+     *
+     * @tparam Component Type of component to get
+     * @return A reference to the component
+     */
+    template <typename Component>
+    Component &get() ENTT_NOEXCEPT {
+        assert(has<Component>());
+        return static_cast<Storage<Component> *>(comps[type<Component>()].get())->comp;
+    }
+    
+    /**
+     * @brief Replaces the given component
+     *
+     * @warning
+     * An assertion will abort the execution at runtime in debug mode in case
+     * the prototype doesn't own the given component
+     *
+     * @tparam Component Type of component to replace
+     * @tparam Args Types of arguments to use to construct the component
+     * @param args Parameters to use to initialize the component
+     * @return A refernce to the newly created component
+     */
+    template <typename Component, typename... Args>
+    Component &replace(Args &&... args) ENTT_NOEXCEPT {
+        return (get<Component>() = Component{std::forward<Args>(args)...});
+    }
+    
+    /**
+     * @brief Assigns of replaces the given component
+     *
+     * @tparam Component Type of component to replace
+     * @tparam Args Types of arguments to use to construct the component
+     * @param args Parameters to use to initialize the component
+     * @return A refernce to the newly created component
+     */
+    template <typename Component, typename... Args>
+    Component &accommodate(Args &&... args) ENTT_NOEXCEPT {
+        if (has<Component>()) {
+            return replace<Component>(std::forward<Args>(args)...);
+        } else {
+            return assign<Component>(std::forward<Args>(args)...);
+        }
+    }
+    
+private:
+    std::vector<std::unique_ptr<StorageBase>> comps;
+};
+
+/**
+ * @brief Default prototype
+ */
+using DefaultPrototype = Prototype<uint32_t>;
+
+}
+
+#endif