#include <iostream>
#include <type_traits>
 
template<typename T>
struct has_size_method
{
private:
	typedef std::true_type yes;
	typedef std::false_type no;
 
	template<typename U, int (U::*f)() const> struct SFINAE{};
	template<typename U, std::size_t (U::*f)() const> struct SFINAE<U,f>{};
 
 
	template<class C> static yes test(SFINAE<C,&C::size>*);
	template<class C> static no test(...);
 
public:
	static constexpr bool value = std::is_same<yes,decltype(test<T>(nullptr))>::value;
};
 
struct x
{
	int size() const { return 42; }
};
 
struct y : x {};
 
int main()
{
	std::cout << has_size_method<x>::value << std::endl;
	std::cout << has_size_method<y>::value << std::endl;
}
 

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