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_COMPOSE_H
11 #define _LIBCPP___FUNCTIONAL_COMPOSE_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 
19 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
20 #  pragma GCC system_header
21 #endif
22 
23 _LIBCPP_BEGIN_NAMESPACE_STD
24 
25 #if _LIBCPP_STD_VER >= 20
26 
27 struct __compose_op {
28   template <class _Fn1, class _Fn2, class... _Args>
29   _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Fn1&& __f1, _Fn2&& __f2, _Args&&... __args) const noexcept(noexcept(
30       std::invoke(std::forward<_Fn1>(__f1), std::invoke(std::forward<_Fn2>(__f2), std::forward<_Args>(__args)...))))
31       -> decltype(std::invoke(std::forward<_Fn1>(__f1),
32                               std::invoke(std::forward<_Fn2>(__f2), std::forward<_Args>(__args)...))) {
33     return std::invoke(std::forward<_Fn1>(__f1), std::invoke(std::forward<_Fn2>(__f2), std::forward<_Args>(__args)...));
34   }
35 };
36 
37 template <class _Fn1, class _Fn2>
38 struct __compose_t : __perfect_forward<__compose_op, _Fn1, _Fn2> {
39   using __perfect_forward<__compose_op, _Fn1, _Fn2>::__perfect_forward;
40 };
41 
42 template <class _Fn1, class _Fn2>
43 _LIBCPP_HIDE_FROM_ABI constexpr auto __compose(_Fn1&& __f1, _Fn2&& __f2) noexcept(
44     noexcept(__compose_t<decay_t<_Fn1>, decay_t<_Fn2>>(std::forward<_Fn1>(__f1), std::forward<_Fn2>(__f2))))
45     -> decltype(__compose_t<decay_t<_Fn1>, decay_t<_Fn2>>(std::forward<_Fn1>(__f1), std::forward<_Fn2>(__f2))) {
46   return __compose_t<decay_t<_Fn1>, decay_t<_Fn2>>(std::forward<_Fn1>(__f1), std::forward<_Fn2>(__f2));
47 }
48 
49 #endif // _LIBCPP_STD_VER >= 20
50 
51 _LIBCPP_END_NAMESPACE_STD
52 
53 #endif // _LIBCPP___FUNCTIONAL_COMPOSE_H
54