#include <iostream>
#include <type_traits>
 
 
struct A {
  using my_tag = void;
};
 
struct B {};
 
struct C {
  using my_tag = int; // with void_t also works with my_tag = int
};
 
struct D {
  struct my_tag{}; //or some tested struct
};
 
// same as your enable_if_type
template <typename...>
using void_t = void;
 
 
template<class T, class Enable = void>
struct has_my_tag : std::false_type {};
 
template<class T>
struct has_my_tag<T, void_t<typename T::my_tag>> : std::true_type
{};
 
 
int main() {
	std::cout << has_my_tag<A>::value << std::endl;
	std::cout << has_my_tag<B>::value << std::endl;
	std::cout << has_my_tag<C>::value << std::endl;
	std::cout << has_my_tag<D>::value << std::endl;
	return 0;
}

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