libcxx/include/__functional/invoke.h

   1 // -*- C++ -*-
   2 //===----------------------------------------------------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #ifndef _LIBCPP___FUNCTIONAL_INVOKE_H
  11 #define _LIBCPP___FUNCTIONAL_INVOKE_H
  12
  13 #include <__config>
  14 #include <__type_traits/invoke.h>
  15 #include <__type_traits/is_void.h>
  16 #include <__utility/forward.h>
  17
  18 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  19 #  pragma GCC system_header
  20 #endif
  21
  22 _LIBCPP_BEGIN_NAMESPACE_STD
  23
  24 #if _LIBCPP_STD_VER >= 17
  25
  26 template <class _Fn, class... _Args>
  27 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 invoke_result_t<_Fn, _Args...>
  28 invoke(_Fn&& __f, _Args&&... __args) noexcept(is_nothrow_invocable_v<_Fn, _Args...>) {
  29   return std::__invoke(std::forward<_Fn>(__f), std::forward<_Args>(__args)...);
  30 }
  31
  32 #endif // _LIBCPP_STD_VER >= 17
  33
  34 #if _LIBCPP_STD_VER >= 23
  35 template <class _Result, class _Fn, class... _Args>
  36   requires is_invocable_r_v<_Result, _Fn, _Args...>
  37 _LIBCPP_HIDE_FROM_ABI constexpr _Result
  38 invoke_r(_Fn&& __f, _Args&&... __args) noexcept(is_nothrow_invocable_r_v<_Result, _Fn, _Args...>) {
  39   if constexpr (is_void_v<_Result>) {
  40     static_cast<void>(std::invoke(std::forward<_Fn>(__f), std::forward<_Args>(__args)...));
  41   } else {
  42     // TODO: Use reference_converts_from_temporary_v once implemented
  43     // using _ImplicitInvokeResult = invoke_result_t<_Fn, _Args...>;
  44     // static_assert(!reference_converts_from_temporary_v<_Result, _ImplicitInvokeResult>,
  45     static_assert(true,
  46                   "Returning from invoke_r would bind a temporary object to the reference return type, "
  47                   "which would result in a dangling reference.");
  48     return std::invoke(std::forward<_Fn>(__f), std::forward<_Args>(__args)...);
  49   }
  50 }
  51 #endif
  52
  53 _LIBCPP_END_NAMESPACE_STD
  54
  55 #endif // _LIBCPP___FUNCTIONAL_INVOKE_H