1// PR c++/67130 2// { dg-do compile { target c++14 } } 3 4namespace std { 5template <typename> struct __success_type; 6template <typename> void declval(); 7template <typename> class decay { 8public: 9 typedef int type; 10}; 11template <typename...> struct common_type; 12struct A { 13 template <typename, typename _Up> 14 static __success_type<typename decay<decltype(declval<_Up>)>::type> _S_test; 15}; 16template <typename _Tp, typename _Up> struct __common_type_impl : A { 17 typedef decltype(_S_test<_Tp, _Up>) type; 18}; 19template <typename _Tp, typename _Up> 20struct common_type<_Tp, _Up> : __common_type_impl<_Tp, _Up> {}; 21} 22template <typename> struct B { struct _; }; 23template <typename T> typename B<T>::_ type; 24template <template <typename...> class> struct C; 25template <template <typename...> class f> C<f> metafunction; 26template <typename T> struct B<T>::_ {}; 27namespace detail { 28template <typename> struct _decltype; 29} 30template <template <typename...> class F> struct C { 31 template <typename... T> 32 auto operator()(T...) 33 -> decltype(type<typename F<detail::_decltype<T>...>::type>); 34}; 35auto common_type = metafunction<std::common_type>(0, 0); 36