C++ awesome.cpp

#include <iostream>

#include <boost/utility.hpp>
#include <boost/type_traits.hpp>

#include <boost/preprocessor/punctuation/comma_if.hpp>
#include <boost/preprocessor/repetition/repeat.hpp>

#define ENTITY_MAX_COMPONENT_COUNT 10
#define ENTITY_TYPENAMES(z, n, text) BOOST_PP_COMMA_IF(n) text##n
#define ENTITY_DEFINE_COMPONENT(z, n, text) T##n text##n;
#define ENTITY_DEFINE_ENTITY_SETTER(z, n, text) component##n.text(*this);

#define ENTITY_DEFINE_COMPONENT_GETTER(z, n, text) \
    template<class INNER_T> \
    typename boost::enable_if<boost::is_base_of<T##n, INNER_T>, INNER_T>::type & text() \
    { \
        return component##n;\
    }

#define ENTITY_DECLARATION(z, n, text) \
    template<BOOST_PP_REPEAT(n, ENTITY_TYPENAMES, class T)> \
    class text<BOOST_PP_REPEAT(n, ENTITY_TYPENAMES, T)> : public Entity \
    { \
        BOOST_PP_REPEAT(n, ENTITY_DEFINE_COMPONENT, component)\
        public: \
            text(const std::string &name) : Entity(name) \
            { \
                BOOST_PP_REPEAT(n, ENTITY_DEFINE_ENTITY_SETTER, setEntity)\
            } \
            BOOST_PP_REPEAT(n, ENTITY_DEFINE_COMPONENT_GETTER, get) \
    };

class Entity
{
    std::string mName;

    public:
        Entity(const std::string &name) : mName(name)
        {
        }

        const std::string &getName() const
        {
            return mName;
        }
};

template <typename ...Dummy>
class SmartEntity;

BOOST_PP_REPEAT(ENTITY_MAX_COMPONENT_COUNT, ENTITY_DECLARATION, SmartEntity)

class Component
{
    const Entity *mEntity;

    public:
        void setEntity(const Entity &value)
        {
            mEntity = &value;
        }

        const Entity &getEntity()
        {
            return *mEntity;
        }
};

class Component1 : public Component
{
    public:
        void some(){ std::cout << "Call Component1::some() of " << getEntity().getName() << std::endl; }
};

class Component2 : public Component
{
    public:
        void otherSome(){ std::cout << "Call Component2::some() of " << getEntity().getName() << std::endl; }
};

int main()
{
    SmartEntity<Component1, Component2> entity("Entity_with_2_components");
    entity.get<Component1>().some();
    entity.get<Component2>().otherSome();
}