v1/__coroutine/coroutine_traits.h

0001 //===----------------------------------------------------------------------===//
0002 //
0003 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
0004 // See https://llvm.org/LICENSE.txt for license information.
0005 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
0006 //
0007 //===----------------------------------------------------------------------===//
0008
0009 #ifndef _LIBCPP___COROUTINE_COROUTINE_TRAITS_H
0010 #define _LIBCPP___COROUTINE_COROUTINE_TRAITS_H
0011
0012 #include <__config>
0013 #include <__type_traits/void_t.h>
0014
0015 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0016 #  pragma GCC system_header
0017 #endif
0018
0019 #if _LIBCPP_STD_VER >= 20
0020
0021 _LIBCPP_BEGIN_NAMESPACE_STD
0022
0023 // [coroutine.traits]
0024 // [coroutine.traits.primary]
0025 //   The header <coroutine> defined the primary template coroutine_traits such that
0026 // if ArgTypes is a parameter pack of types and if the qualified-id R::promise_type
0027 // is valid and denotes a type ([temp.deduct]), then coroutine_traits<R, ArgTypes...>
0028 // has the following publicly accessible memebr:
0029 //
0030 //    using promise_type = typename R::promise_type;
0031 //
0032 // Otherwise, coroutine_traits<R, ArgTypes...> has no members.
0033 template <class _Tp, class = void>
0034 struct __coroutine_traits_sfinae {};
0035
0036 template <class _Tp>
0037 struct __coroutine_traits_sfinae< _Tp, __void_t<typename _Tp::promise_type> > {
0038   using promise_type = typename _Tp::promise_type;
0039 };
0040
0041 template <class _Ret, class... _Args>
0042 struct coroutine_traits : public __coroutine_traits_sfinae<_Ret> {};
0043
0044 _LIBCPP_END_NAMESPACE_STD
0045
0046 #endif // __LIBCPP_STD_VER >= 20
0047
0048 #endif // _LIBCPP___COROUTINE_COROUTINE_TRAITS_H