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