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 <__utility/forward.h>
17 #include <type_traits>
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 > 17
26 
27 struct __compose_op {
28     template<class _Fn1, class _Fn2, class ..._Args>
29     _LIBCPP_HIDE_FROM_ABI
30     constexpr auto operator()(_Fn1&& __f1, _Fn2&& __f2, _Args&&... __args) const
31         noexcept(noexcept(_VSTD::invoke(_VSTD::forward<_Fn1>(__f1), _VSTD::invoke(_VSTD::forward<_Fn2>(__f2), _VSTD::forward<_Args>(__args)...))))
32         -> decltype(      _VSTD::invoke(_VSTD::forward<_Fn1>(__f1), _VSTD::invoke(_VSTD::forward<_Fn2>(__f2), _VSTD::forward<_Args>(__args)...)))
33         { return          _VSTD::invoke(_VSTD::forward<_Fn1>(__f1), _VSTD::invoke(_VSTD::forward<_Fn2>(__f2), _VSTD::forward<_Args>(__args)...)); }
34 };
35 
36 template <class _Fn1, class _Fn2>
37 struct __compose_t : __perfect_forward<__compose_op, _Fn1, _Fn2> {
38     using __perfect_forward<__compose_op, _Fn1, _Fn2>::__perfect_forward;
39 };
40 
41 template <class _Fn1, class _Fn2>
42 _LIBCPP_HIDE_FROM_ABI
43 constexpr auto __compose(_Fn1&& __f1, _Fn2&& __f2)
44     noexcept(noexcept(__compose_t<decay_t<_Fn1>, decay_t<_Fn2>>(_VSTD::forward<_Fn1>(__f1), _VSTD::forward<_Fn2>(__f2))))
45     -> decltype(      __compose_t<decay_t<_Fn1>, decay_t<_Fn2>>(_VSTD::forward<_Fn1>(__f1), _VSTD::forward<_Fn2>(__f2)))
46     { return          __compose_t<decay_t<_Fn1>, decay_t<_Fn2>>(_VSTD::forward<_Fn1>(__f1), _VSTD::forward<_Fn2>(__f2)); }
47 
48 #endif // _LIBCPP_STD_VER > 17
49 
50 _LIBCPP_END_NAMESPACE_STD
51 
52 #endif // _LIBCPP___FUNCTIONAL_COMPOSE_H
53