mixclass.cpp

#include <iostream>
#if 0
#define BINDABLE                                                               \
    template<typename Type1, typename Type2>                                   \
    friend void* bind(const Type1& t1, const Type2& t2);                       \
                                                                               \
    template<typename Type1, typename Type2>                                   \
    friend void* bind(Type1* t1, Type2* t2);                                   \
                                                                               \
    template<typename Type1, typename Type2>                                   \
    friend void* bind(Type1 const &t1, Type2 const& t2);                       \
                                                                               \
    template<typename Type1, typename Type2>                                   \
    friend void* bind(Type1 t1, Type2 t2);

#endif

#define BINDABLE                                                               \
    template<typename Type1, typename Type2>                                   \
    friend void* bind(Type1* t1, Type2* t2);                                   \
                                                                               \
    template<typename Type1, typename Type2>                                   \
    friend void* bind(const Type1& t1, const Type2& t2);


class A
{
    BINDABLE
    int a;
public:
    A(const A& ref) = default ; // test std::is_trivially_copy_constructible<>(.T.)
    A() : a (20) {}
    ~A() {}

};


class B
{
    BINDABLE
    int b;
public:
    B(const B& ref) = default ;
    B() : b(10) {}
    ~B() {}

};



template<>
void* bind(A a, B b)
{
    std::cout << "Called by value\r\n";
    std::cout << "[" << a.a + b.b << "]\r\n";
}

template<>
void* bind(const A& a, const B& b)
{
    std::cout << "Called by ref\r\n";
    std::cout << "[" << a.a + b.b << "]\r\n";
}

template<>
void* bind(A* a, B* b)
{
    std::cout << "Called by ptr\r\n";
    std::cout << "[" << a->a + b->b << "]\r\n";
}


template <class T>
struct U
{
    typename std::enable_if<std::is_union<T>{}, T>::type m_ref;
    U(const T& ref) : m_ref{ref} { }
};


union tst
{
    int val;
};

int main()
{
    A a;
    B b;

    tst vvv = {10};

    U<tst> rrr {vvv};

    bind(a, b);

}