libcxx/include/__functional/perfect_forward.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_PERFECT_FORWARD_H
  11 #define _LIBCPP___FUNCTIONAL_PERFECT_FORWARD_H
  12
  13 #include <__config>
  14 #include <__type_traits/enable_if.h>
  15 #include <__type_traits/invoke.h>
  16 #include <__type_traits/is_constructible.h>
  17 #include <__utility/declval.h>
  18 #include <__utility/forward.h>
  19 #include <__utility/integer_sequence.h>
  20 #include <__utility/move.h>
  21 #include <tuple>
  22
  23 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  24 #  pragma GCC system_header
  25 #endif
  26
  27 _LIBCPP_PUSH_MACROS
  28 #include <__undef_macros>
  29
  30 _LIBCPP_BEGIN_NAMESPACE_STD
  31
  32 #if _LIBCPP_STD_VER >= 17
  33
  34 template <class _Op, class _Indices, class... _BoundArgs>
  35 struct __perfect_forward_impl;
  36
  37 template <class _Op, size_t... _Idx, class... _BoundArgs>
  38 struct __perfect_forward_impl<_Op, index_sequence<_Idx...>, _BoundArgs...> {
  39 private:
  40   tuple<_BoundArgs...> __bound_args_;
  41
  42 public:
  43   template <class... _Args, class = enable_if_t< is_constructible_v<tuple<_BoundArgs...>, _Args&&...> >>
  44   _LIBCPP_HIDE_FROM_ABI explicit constexpr __perfect_forward_impl(_Args&&... __bound_args)
  45       : __bound_args_(std::forward<_Args>(__bound_args)...) {}
  46
  47   _LIBCPP_HIDE_FROM_ABI __perfect_forward_impl(__perfect_forward_impl const&) = default;
  48   _LIBCPP_HIDE_FROM_ABI __perfect_forward_impl(__perfect_forward_impl&&)      = default;
  49
  50   _LIBCPP_HIDE_FROM_ABI __perfect_forward_impl& operator=(__perfect_forward_impl const&) = default;
  51   _LIBCPP_HIDE_FROM_ABI __perfect_forward_impl& operator=(__perfect_forward_impl&&)      = default;
  52
  53   template <class... _Args, class = enable_if_t<is_invocable_v<_Op, _BoundArgs&..., _Args...>>>
  54   _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Args&&... __args) & noexcept(
  55       noexcept(_Op()(std::get<_Idx>(__bound_args_)..., std::forward<_Args>(__args)...)))
  56       -> decltype(_Op()(std::get<_Idx>(__bound_args_)..., std::forward<_Args>(__args)...)) {
  57     return _Op()(std::get<_Idx>(__bound_args_)..., std::forward<_Args>(__args)...);
  58   }
  59
  60   template <class... _Args, class = enable_if_t<!is_invocable_v<_Op, _BoundArgs&..., _Args...>>>
  61   auto operator()(_Args&&...) & = delete;
  62
  63   template <class... _Args, class = enable_if_t<is_invocable_v<_Op, _BoundArgs const&..., _Args...>>>
  64   _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Args&&... __args) const& noexcept(
  65       noexcept(_Op()(std::get<_Idx>(__bound_args_)..., std::forward<_Args>(__args)...)))
  66       -> decltype(_Op()(std::get<_Idx>(__bound_args_)..., std::forward<_Args>(__args)...)) {
  67     return _Op()(std::get<_Idx>(__bound_args_)..., std::forward<_Args>(__args)...);
  68   }
  69
  70   template <class... _Args, class = enable_if_t<!is_invocable_v<_Op, _BoundArgs const&..., _Args...>>>
  71   auto operator()(_Args&&...) const& = delete;
  72
  73   template <class... _Args, class = enable_if_t<is_invocable_v<_Op, _BoundArgs..., _Args...>>>
  74   _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Args&&... __args) && noexcept(
  75       noexcept(_Op()(std::get<_Idx>(std::move(__bound_args_))..., std::forward<_Args>(__args)...)))
  76       -> decltype(_Op()(std::get<_Idx>(std::move(__bound_args_))..., std::forward<_Args>(__args)...)) {
  77     return _Op()(std::get<_Idx>(std::move(__bound_args_))..., std::forward<_Args>(__args)...);
  78   }
  79
  80   template <class... _Args, class = enable_if_t<!is_invocable_v<_Op, _BoundArgs..., _Args...>>>
  81   auto operator()(_Args&&...) && = delete;
  82
  83   template <class... _Args, class = enable_if_t<is_invocable_v<_Op, _BoundArgs const..., _Args...>>>
  84   _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Args&&... __args) const&& noexcept(
  85       noexcept(_Op()(std::get<_Idx>(std::move(__bound_args_))..., std::forward<_Args>(__args)...)))
  86       -> decltype(_Op()(std::get<_Idx>(std::move(__bound_args_))..., std::forward<_Args>(__args)...)) {
  87     return _Op()(std::get<_Idx>(std::move(__bound_args_))..., std::forward<_Args>(__args)...);
  88   }
  89
  90   template <class... _Args, class = enable_if_t<!is_invocable_v<_Op, _BoundArgs const..., _Args...>>>
  91   auto operator()(_Args&&...) const&& = delete;
  92 };
  93
  94 // __perfect_forward implements a perfect-forwarding call wrapper as explained in [func.require].
  95 template <class _Op, class... _Args>
  96 using __perfect_forward = __perfect_forward_impl<_Op, index_sequence_for<_Args...>, _Args...>;
  97
  98 #endif // _LIBCPP_STD_VER >= 17
  99
 100 _LIBCPP_END_NAMESPACE_STD
 101
 102 _LIBCPP_POP_MACROS
 103
 104 #endif // _LIBCPP___FUNCTIONAL_PERFECT_FORWARD_H