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_FRONT_H
11 #define _LIBCPP___FUNCTIONAL_BIND_FRONT_H
12 
13 #include <__config>
14 #include <__functional/invoke.h>
15 #include <__functional/perfect_forward.h>
16 #include <__type_traits/conjunction.h>
17 #include <__type_traits/decay.h>
18 #include <__type_traits/enable_if.h>
19 #include <__type_traits/is_constructible.h>
20 #include <__type_traits/is_move_constructible.h>
21 #include <__utility/forward.h>
22 
23 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
24 #  pragma GCC system_header
25 #endif
26 
27 _LIBCPP_BEGIN_NAMESPACE_STD
28 
29 #if _LIBCPP_STD_VER >= 20
30 
31 struct __bind_front_op {
32   template <class... _Args>
33   _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Args&&... __args) const
34       noexcept(noexcept(std::invoke(std::forward<_Args>(__args)...)))
35           -> decltype(std::invoke(std::forward<_Args>(__args)...)) {
36     return std::invoke(std::forward<_Args>(__args)...);
37   }
38 };
39 
40 template <class _Fn, class... _BoundArgs>
41 struct __bind_front_t : __perfect_forward<__bind_front_op, _Fn, _BoundArgs...> {
42   using __perfect_forward<__bind_front_op, _Fn, _BoundArgs...>::__perfect_forward;
43 };
44 
45 template <class _Fn, class... _Args>
46   requires is_constructible_v<decay_t<_Fn>, _Fn> && is_move_constructible_v<decay_t<_Fn>> &&
47            (is_constructible_v<decay_t<_Args>, _Args> && ...) && (is_move_constructible_v<decay_t<_Args>> && ...)
48 _LIBCPP_HIDE_FROM_ABI constexpr auto bind_front(_Fn&& __f, _Args&&... __args) {
49   return __bind_front_t<decay_t<_Fn>, decay_t<_Args>...>(std::forward<_Fn>(__f), std::forward<_Args>(__args)...);
50 }
51 
52 #endif // _LIBCPP_STD_VER >= 20
53 
54 _LIBCPP_END_NAMESPACE_STD
55 
56 #endif // _LIBCPP___FUNCTIONAL_BIND_FRONT_H
57