libcxx/include/__functional/compose.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_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