1// PR c++/59204 2// { dg-do compile { target c++11 } } 3 4template< class T > 5 using void_t = void; 6 7template< class T, class = void > 8 struct has_type 9{ constexpr static bool value = false; }; 10 11template< class T > 12 struct has_type<T, void_t<typename T::type>> 13{ constexpr static bool value = true; }; 14 15struct yes { using type = int; }; 16struct no { }; 17 18int 19main( ) 20{ 21 static_assert( has_type<yes>::value, "false negative!" ); 22 static_assert( not has_type<no >::value, "false positive!" ); 23} 24