Question

我正在尝试将一些称为组件的数据附加到实体节点。但是，每当我将派生组件类型附加到Entity节点时，它都会被提升为基本Component类型而不是保留子节点。我怎么能阻止这个，所以我可以使用std::type_index？目前，由于组件正在升级，std::type_index不断为Component创建索引，而不是其中一个子类。我是否需要模板AttachComponent方法？我不愿意。

class Entity final
    {
        //Typedefs
        typedef std::map<std::type_index, std::shared_ptr<acorn::Component> > ComponentMap;


        ComponentMap m_components;
        unsigned long int m_ID;

    private:


    public:
        explicit Entity(unsigned long int id);
        ~Entity();

        //Getters
        inline unsigned long int GetID() const
        {
            return m_ID;
        }

        template<class ComponentType>
        std::weak_ptr<ComponentType> GetComponent()
        {

            auto component_map_it = m_components.find(std::type_index(typeid(ComponentType)));
            //If the component was found
            if (component_map_it != m_components.end()) {
                //Get the shared_ptr of the component
                std::shared_ptr<acorn::Component> base_ptr = component_map_it->second;
                //Cast it to the desired component type
                std::shared_ptr<ComponentType> converted_ptr(std::static_pointer_cast<ComponentType>(base_ptr));
                //Convert to a weak pointer
                std::weak_ptr<ComponentType> return_ptr(converted_ptr);

                //Return the weak pointer
                return return_ptr;
            } 
            else {
                //If no component type was found, return a nullptr.
                return  std::weak_ptr<ComponentType>();
            }

        }

        //Setters
        inline void AttachComponent(std::shared_ptr<Component> component)
        {
            auto raw_ptr = component.get();
            auto insert_pair = std::make_pair(std::type_index(typeid(raw_ptr)), component);
            m_components.insert(insert_pair);
        }

    };`

Answer 1

是的，你必须让AttachComponent成为一个模板。这是保留类型信息的唯一方法：

template <class T>
void AttachComponent(std::shared_ptr<T> component)
{
  // as before
}

Shared_Ptr <derived>被上传到Shared_Ptr <base />

1 个答案: