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 <__utility/forward.h>
  16
  17 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  18 #  pragma GCC system_header
  19 #endif
  20
  21 _LIBCPP_BEGIN_NAMESPACE_STD
  22
  23 #if _LIBCPP_STD_VER >= 17
  24
  25 template <class _Fn, class ..._Args>
  26 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 invoke_result_t<_Fn, _Args...>
  27 invoke(_Fn&& __f, _Args&&... __args)
  28     noexcept(is_nothrow_invocable_v<_Fn, _Args...>)
  29 {
  30     return _VSTD::__invoke(_VSTD::forward<_Fn>(__f), _VSTD::forward<_Args>(__args)...);
  31 }
  32
  33 #endif // _LIBCPP_STD_VER >= 17
  34
  35 #if _LIBCPP_STD_VER >= 23
  36 template <class _Result, class _Fn, class... _Args>
  37   requires is_invocable_r_v<_Result, _Fn, _Args...>
  38 _LIBCPP_HIDE_FROM_ABI constexpr _Result
  39 invoke_r(_Fn&& __f, _Args&&... __args) noexcept(is_nothrow_invocable_r_v<_Result, _Fn, _Args...>) {
  40     if constexpr (is_void_v<_Result>) {
  41         static_cast<void>(std::invoke(std::forward<_Fn>(__f), std::forward<_Args>(__args)...));
  42     } else {
  43         // TODO: Use reference_converts_from_temporary_v once implemented
  44         // using _ImplicitInvokeResult = invoke_result_t<_Fn, _Args...>;
  45         // static_assert(!reference_converts_from_temporary_v<_Result, _ImplicitInvokeResult>,
  46         static_assert(true,
  47             "Returning from invoke_r would bind a temporary object to the reference return type, "
  48             "which would result in a dangling reference.");
  49         return std::invoke(std::forward<_Fn>(__f), std::forward<_Args>(__args)...);
  50     }
  51 }
  52 #endif
  53
  54 _LIBCPP_END_NAMESPACE_STD
  55
  56 #endif // _LIBCPP___FUNCTIONAL_INVOKE_H