Has Member Template

has_member.cpp

#include <type_traits>
#include <iostream>
#include <iomanip>

#define DECLARE_HAS_MEMBER(member)                                                \
                                                                                  \
template < class T >                                                              \
class HasMember_##member                                                          \
{                                                                                 \
private:                                                                          \
    using Yes = char[2];                                                          \
    using  No = char[1];                                                          \
                                                                                  \
    struct Fallback { int member; };                                              \
    struct Derived : T, Fallback { };                                             \
                                                                                  \
    template < class U >                                                          \
    static No& test ( decltype(U::member)* );                                     \
    template < typename U >                                                       \
    static Yes& test ( ... );                                                     \
                                                                                  \
public:                                                                           \
    static constexpr bool RESULT = sizeof(test<Derived>(nullptr)) == sizeof(Yes); \
};                                                                                \
                                                                                  \
template < class T >                                                              \
struct has_member_##member                                                        \
: public std::integral_constant<bool, HasMember_##member<T>::RESULT>              \
{ };                                                                              \
 
 
DECLARE_HAS_MEMBER(draw);

struct drawable {
	void draw() { }
};

struct dribable {
	void dribble() { }
};

int main(int argc, char *argv[]) {
	using namespace std;

	cout << "drawable has draw()? " << has_member_draw<drawable>() << endl;
	cout << "dribable has draw()? " << has_member_draw<dribable>() << endl;

	return 0;
}