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