Ex.hpp

enum class ComponentType : unsigned
{
  Invalid,
  Transform,
}

class Component 
{
virtual ComponentType GetType() const = 0;
};

#define COMPONENT_TYPE(Type)                                 \
public:                                                      \
  ComponentType StaticType() { return Type; }                \
  ComponentType GetType() override { return StaticType(); } 

class TransformComponent : public Component
{
  COMPONENT_TYPE(ComponentType::Transform)
public:
  void SetPosition(...);
};

class Entity 
{
public:
  template <typename T>
  T* GetComponent() const 
  {
    ComponentType key = T::StaticType();
    Component* value = m_components[ key ];
    return static_cast<T*>(value);
  }
  
  template <typename T, typename... Args>
  T* AddComponent(Args&&... inArgs) 
  {
    Component*& newComponent = m_components[ key ];
    newComponent = new T(std::forward<Args>(inArgs)...);
    return static_cast<T*>(newComponent);
  }
private:
  
  std::unordered_map<ComponentType, Component*> m_components;
};