1 // RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify 2 3 // This is a test for an egregious hack in Clang that works around 4 // an issue with GCC's <type_traits> implementation. std::common_type 5 // relies on pre-standard rules for decltype(), in which it doesn't 6 // produce reference types so frequently. 7 8 #ifdef BE_THE_HEADER 9 10 #pragma GCC system_header 11 namespace std { 12 template<typename T> T &&declval(); 13 14 template<typename...Ts> struct common_type {}; 15 template<typename A, typename B> struct common_type<A, B> { 16 // Under the rules in the standard, this always produces a 17 // reference type. 18 typedef decltype(true ? declval<A>() : declval<B>()) type; 19 }; 20 } 21 22 #else 23 24 #define BE_THE_HEADER 25 #include "libstdcxx_common_type_hack.cpp" 26 27 using T = int; 28 using T = std::common_type<int, int>::type; 29 30 using U = int; // expected-note {{here}} 31 using U = decltype(true ? std::declval<int>() : std::declval<int>()); // expected-error {{different types}} 32 33 #endif 34
