C++ static "has_function" with SFINAE

c++_has_function.cpp

#include <iostream>

struct Foo
{
	void One();
};

struct Baz : Foo
{
	void Two();
};

struct Bar
{
	int One(int);
};

template <class T>
struct HasOne
{
	typedef char Yes[1];
	typedef char No[2];

	template <typename U, U>
	struct Check;

	template <typename C>
	static Yes & Test(Check<void (C::*)(), &C::One> *);
	
	template <typename>
	static No & Test(...);

	static const bool value = sizeof(Test<T>(0)) == sizeof(Yes);
};

int main()
{
	std::cout << HasOne<Foo>::value << std::endl; // 1
	std::cout << HasOne<Bar>::value << std::endl; // 0
	std::cout << HasOne<Baz>::value << std::endl; // 0
};