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/invoke.h>
  20 #include <__type_traits/is_member_pointer.h>
  21 #include <__type_traits/is_same.h>
  22 #include <__utility/declval.h>
  23 #include <__utility/forward.h>
  24
  25 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  26 #  pragma GCC system_header
  27 #endif
  28
  29 _LIBCPP_BEGIN_NAMESPACE_STD
  30
  31 template <class _Pred, class _Proj>
  32 struct _ProjectedPred {
  33   _Pred& __pred; // Can be a unary or a binary predicate.
  34   _Proj& __proj;
  35
  36   _LIBCPP_CONSTEXPR _LIBCPP_HIDE_FROM_ABI _ProjectedPred(_Pred& __pred_arg, _Proj& __proj_arg)
  37       : __pred(__pred_arg), __proj(__proj_arg) {}
  38
  39   template <class _Tp>
  40   typename __invoke_of<_Pred&, decltype(std::__invoke(std::declval<_Proj&>(), std::declval<_Tp>()))>::type
  41       _LIBCPP_CONSTEXPR _LIBCPP_HIDE_FROM_ABI
  42       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>()))>::type _LIBCPP_CONSTEXPR
  50   _LIBCPP_HIDE_FROM_ABI
  51   operator()(_T1&& __lhs, _T2&& __rhs) const {
  52     return std::__invoke(
  53         __pred, std::__invoke(__proj, std::forward<_T1>(__lhs)), std::__invoke(__proj, std::forward<_T2>(__rhs)));
  54   }
  55 };
  56
  57 template <
  58     class _Pred,
  59     class _Proj,
  60     __enable_if_t<!(!is_member_pointer<__decay_t<_Pred> >::value && __is_identity<__decay_t<_Proj> >::value), int> = 0>
  61 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _ProjectedPred<_Pred, _Proj> __make_projected(_Pred& __pred, _Proj& __proj) {
  62   return _ProjectedPred<_Pred, _Proj>(__pred, __proj);
  63 }
  64
  65 // Avoid creating the functor and just use the pristine comparator -- for certain algorithms, this would enable
  66 // optimizations that rely on the type of the comparator. Additionally, this results in less layers of indirection in
  67 // the call stack when the comparator is invoked, even in an unoptimized build.
  68 template <
  69     class _Pred,
  70     class _Proj,
  71     __enable_if_t<!is_member_pointer<__decay_t<_Pred> >::value && __is_identity<__decay_t<_Proj> >::value, int> = 0>
  72 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _Pred& __make_projected(_Pred& __pred, _Proj&) {
  73   return __pred;
  74 }
  75
  76 _LIBCPP_END_NAMESPACE_STD
  77
  78 #if _LIBCPP_STD_VER >= 20
  79
  80 _LIBCPP_BEGIN_NAMESPACE_STD
  81
  82 namespace ranges {
  83
  84 template <class _Comp, class _Proj1, class _Proj2>
  85 _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) __make_projected_comp(_Comp& __comp, _Proj1& __proj1, _Proj2& __proj2) {
  86   if constexpr (__is_identity<decay_t<_Proj1>>::value && __is_identity<decay_t<_Proj2>>::value &&
  87                 !is_member_pointer_v<decay_t<_Comp>>) {
  88     // Avoid creating the lambda and just use the pristine comparator -- for certain algorithms, this would enable
  89     // optimizations that rely on the type of the comparator.
  90     return __comp;
  91
  92   } else {
  93     return [&](auto&& __lhs, auto&& __rhs) -> bool {
  94       return std::invoke(__comp,
  95                          std::invoke(__proj1, std::forward<decltype(__lhs)>(__lhs)),
  96                          std::invoke(__proj2, std::forward<decltype(__rhs)>(__rhs)));
  97     };
  98   }
  99 }
 100
 101 } // namespace ranges
 102
 103 _LIBCPP_END_NAMESPACE_STD
 104
 105 #endif // _LIBCPP_STD_VER >= 20
 106
 107 #endif // _LIBCPP___ALGORITHM_MAKE_PROJECTED_H