libcxx/include/__algorithm/make_projected.h

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef _LIBCPP___ALGORITHM_MAKE_PROJECTED_H
  10 #define _LIBCPP___ALGORITHM_MAKE_PROJECTED_H
  11
  12 #include <__concepts/same_as.h>
  13 #include <__config>
  14 #include <__functional/identity.h>
  15 #include <__functional/invoke.h>
  16 #include <__type_traits/decay.h>
  17 #include <__type_traits/enable_if.h>
  18 #include <__type_traits/integral_constant.h>
  19 #include <__type_traits/is_member_pointer.h>
  20 #include <__type_traits/is_same.h>
  21 #include <__utility/declval.h>
  22 #include <__utility/forward.h>
  23
  24 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  25 #  pragma GCC system_header
  26 #endif
  27
  28 _LIBCPP_BEGIN_NAMESPACE_STD
  29
  30 template <class _Pred, class _Proj>
  31 struct _ProjectedPred {
  32   _Pred& __pred; // Can be a unary or a binary predicate.
  33   _Proj& __proj;
  34
  35   _LIBCPP_CONSTEXPR _LIBCPP_HIDE_FROM_ABI _ProjectedPred(_Pred& __pred_arg, _Proj& __proj_arg)
  36       : __pred(__pred_arg), __proj(__proj_arg) {}
  37
  38   template <class _Tp>
  39   typename __invoke_of<_Pred&,
  40                        decltype(std::__invoke(std::declval<_Proj&>(), std::declval<_Tp>()))
  41   >::type
  42   _LIBCPP_CONSTEXPR _LIBCPP_HIDE_FROM_ABI operator()(_Tp&& __v) const {
  43     return std::__invoke(__pred, std::__invoke(__proj, std::forward<_Tp>(__v)));
  44   }
  45
  46   template <class _T1, class _T2>
  47   typename __invoke_of<_Pred&,
  48                        decltype(std::__invoke(std::declval<_Proj&>(), std::declval<_T1>())),
  49                        decltype(std::__invoke(std::declval<_Proj&>(), std::declval<_T2>()))
  50   >::type
  51   _LIBCPP_CONSTEXPR _LIBCPP_HIDE_FROM_ABI operator()(_T1&& __lhs, _T2&& __rhs) const {
  52     return std::__invoke(__pred,
  53                       std::__invoke(__proj, std::forward<_T1>(__lhs)),
  54                       std::__invoke(__proj, std::forward<_T2>(__rhs)));
  55   }
  56
  57 };
  58
  59 template <class _Pred,
  60           class _Proj,
  61           __enable_if_t<!(!is_member_pointer<__decay_t<_Pred> >::value &&
  62                             __is_identity<__decay_t<_Proj> >::value),
  63                         int> = 0>
  64 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _ProjectedPred<_Pred, _Proj>
  65 __make_projected(_Pred& __pred, _Proj& __proj) {
  66   return _ProjectedPred<_Pred, _Proj>(__pred, __proj);
  67 }
  68
  69 // Avoid creating the functor and just use the pristine comparator -- for certain algorithms, this would enable
  70 // optimizations that rely on the type of the comparator. Additionally, this results in less layers of indirection in
  71 // the call stack when the comparator is invoked, even in an unoptimized build.
  72 template <class _Pred,
  73           class _Proj,
  74           __enable_if_t<!is_member_pointer<__decay_t<_Pred> >::value &&
  75                           __is_identity<__decay_t<_Proj> >::value,
  76                         int> = 0>
  77 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _Pred& __make_projected(_Pred& __pred, _Proj&) {
  78   return __pred;
  79 }
  80
  81 _LIBCPP_END_NAMESPACE_STD
  82
  83 #if _LIBCPP_STD_VER >= 20
  84
  85 _LIBCPP_BEGIN_NAMESPACE_STD
  86
  87 namespace ranges {
  88
  89 template <class _Comp, class _Proj1, class _Proj2>
  90 _LIBCPP_HIDE_FROM_ABI constexpr
  91 decltype(auto) __make_projected_comp(_Comp& __comp, _Proj1& __proj1, _Proj2& __proj2) {
  92   if constexpr (__is_identity<decay_t<_Proj1>>::value && __is_identity<decay_t<_Proj2>>::value &&
  93                 !is_member_pointer_v<decay_t<_Comp>>) {
  94     // Avoid creating the lambda and just use the pristine comparator -- for certain algorithms, this would enable
  95     // optimizations that rely on the type of the comparator.
  96     return __comp;
  97
  98   } else {
  99     return [&](auto&& __lhs, auto&& __rhs) {
 100       return std::invoke(__comp,
 101                         std::invoke(__proj1, std::forward<decltype(__lhs)>(__lhs)),
 102                         std::invoke(__proj2, std::forward<decltype(__rhs)>(__rhs)));
 103     };
 104   }
 105 }
 106
 107 } // namespace ranges
 108
 109 _LIBCPP_END_NAMESPACE_STD
 110
 111 #endif // _LIBCPP_STD_VER >= 20
 112
 113 #endif // _LIBCPP___ALGORITHM_MAKE_PROJECTED_H