1 //===----------------------------------------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #ifndef _LIBCPP___COROUTINE_COROUTINE_TRAITS_H
10 #define _LIBCPP___COROUTINE_COROUTINE_TRAITS_H
11 
12 #include <__config>
13 #include <type_traits>
14 
15 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
16 #pragma GCC system_header
17 #endif
18 
19 #if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_CXX20_COROUTINES)
20 
21 _LIBCPP_BEGIN_NAMESPACE_STD
22 
23 // [coroutine.traits]
24 // [coroutine.traits.primary]
25 //   The header <coroutine> defined the primary template coroutine_traits such that
26 // if ArgTypes is a parameter pack of types and if the qualified-id R::promise_type
27 // is valid and denotes a type ([temp.deduct]), then coroutine_traits<R, ArgTypes...>
28 // has the following publicly accessible memebr:
29 //
30 //    using promise_type = typename R::promise_type;
31 //
32 // Otherwise, coroutine_traits<R, ArgTypes...> has no members.
33 template <class _Tp, class = void>
34 struct __coroutine_traits_sfinae {};
35 
36 template <class _Tp>
37 struct __coroutine_traits_sfinae<
38     _Tp, typename __void_t<typename _Tp::promise_type>::type>
39 {
40   using promise_type = typename _Tp::promise_type;
41 };
42 
43 template <class _Ret, class... _Args>
44 struct coroutine_traits
45     : public __coroutine_traits_sfinae<_Ret>
46 {
47 };
48 
49 _LIBCPP_END_NAMESPACE_STD
50 
51 #endif // __LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_CXX20_COROUTINES)
52 
53 #endif // _LIBCPP___COROUTINE_COROUTINE_TRAITS_H
54