libcxx/include/__functional/bind_back.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_BIND_BACK_H
  11 #define _LIBCPP___FUNCTIONAL_BIND_BACK_H
  12
  13 #include <__config>
  14 #include <__functional/invoke.h>
  15 #include <__functional/perfect_forward.h>
  16 #include <__type_traits/decay.h>
  17 #include <__utility/forward.h>
  18 #include <__utility/integer_sequence.h>
  19 #include <tuple>
  20
  21 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  22 #  pragma GCC system_header
  23 #endif
  24
  25 _LIBCPP_BEGIN_NAMESPACE_STD
  26
  27 #if _LIBCPP_STD_VER >= 20
  28
  29 template <size_t _NBound, class = make_index_sequence<_NBound>>
  30 struct __bind_back_op;
  31
  32 template <size_t _NBound, size_t... _Ip>
  33 struct __bind_back_op<_NBound, index_sequence<_Ip...>> {
  34   template <class _Fn, class _BoundArgs, class... _Args>
  35   _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Fn&& __f, _BoundArgs&& __bound_args, _Args&&... __args) const
  36       noexcept(noexcept(std::invoke(std::forward<_Fn>(__f),
  37                                     std::forward<_Args>(__args)...,
  38                                     std::get<_Ip>(std::forward<_BoundArgs>(__bound_args))...)))
  39           -> decltype(std::invoke(std::forward<_Fn>(__f),
  40                                   std::forward<_Args>(__args)...,
  41                                   std::get<_Ip>(std::forward<_BoundArgs>(__bound_args))...)) {
  42     return std::invoke(std::forward<_Fn>(__f),
  43                        std::forward<_Args>(__args)...,
  44                        std::get<_Ip>(std::forward<_BoundArgs>(__bound_args))...);
  45   }
  46 };
  47
  48 template <class _Fn, class _BoundArgs>
  49 struct __bind_back_t : __perfect_forward<__bind_back_op<tuple_size_v<_BoundArgs>>, _Fn, _BoundArgs> {
  50   using __perfect_forward<__bind_back_op<tuple_size_v<_BoundArgs>>, _Fn, _BoundArgs>::__perfect_forward;
  51 };
  52
  53 template <class _Fn, class... _Args>
  54   requires is_constructible_v<decay_t<_Fn>, _Fn> && is_move_constructible_v<decay_t<_Fn>> &&
  55                (is_constructible_v<decay_t<_Args>, _Args> && ...) && (is_move_constructible_v<decay_t<_Args>> && ...)
  56 _LIBCPP_HIDE_FROM_ABI constexpr auto __bind_back(_Fn&& __f, _Args&&... __args) noexcept(
  57     noexcept(__bind_back_t<decay_t<_Fn>, tuple<decay_t<_Args>...>>(
  58         std::forward<_Fn>(__f), std::forward_as_tuple(std::forward<_Args>(__args)...))))
  59     -> decltype(__bind_back_t<decay_t<_Fn>, tuple<decay_t<_Args>...>>(
  60         std::forward<_Fn>(__f), std::forward_as_tuple(std::forward<_Args>(__args)...))) {
  61   return __bind_back_t<decay_t<_Fn>, tuple<decay_t<_Args>...>>(
  62       std::forward<_Fn>(__f), std::forward_as_tuple(std::forward<_Args>(__args)...));
  63 }
  64
  65 #  if _LIBCPP_STD_VER >= 23
  66 template <class _Fn, class... _Args>
  67 _LIBCPP_HIDE_FROM_ABI constexpr auto bind_back(_Fn&& __f, _Args&&... __args) {
  68   static_assert(is_constructible_v<decay_t<_Fn>, _Fn>, "bind_back requires decay_t<F> to be constructible from F");
  69   static_assert(is_move_constructible_v<decay_t<_Fn>>, "bind_back requires decay_t<F> to be move constructible");
  70   static_assert((is_constructible_v<decay_t<_Args>, _Args> && ...),
  71                 "bind_back requires all decay_t<Args> to be constructible from respective Args");
  72   static_assert((is_move_constructible_v<decay_t<_Args>> && ...),
  73                 "bind_back requires all decay_t<Args> to be move constructible");
  74   return __bind_back_t<decay_t<_Fn>, tuple<decay_t<_Args>...>>(
  75       std::forward<_Fn>(__f), std::forward_as_tuple(std::forward<_Args>(__args)...));
  76 }
  77 #  endif // _LIBCPP_STD_VER >= 23
  78
  79 #endif // _LIBCPP_STD_VER >= 20
  80
  81 _LIBCPP_END_NAMESPACE_STD
  82
  83 #endif // _LIBCPP___FUNCTIONAL_BIND_BACK_H