libcxx/include/__coroutine/coroutine_traits.h

   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/void_t.h>
  14
  15 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  16 #  pragma GCC system_header
  17 #endif
  18
  19 #if _LIBCPP_STD_VER >= 20
  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, __void_t<typename _Tp::promise_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 >= 20
  52
  53 #endif // _LIBCPP___COROUTINE_COROUTINE_TRAITS_H