__cxx03/__algorithm/make_projected.h

0001 //===----------------------------------------------------------------------===//
0002 //
0003 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
0004 // See https://llvm.org/LICENSE.txt for license information.
0005 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
0006 //
0007 //===----------------------------------------------------------------------===//
0008
0009 #ifndef _LIBCPP___CXX03___ALGORITHM_MAKE_PROJECTED_H
0010 #define _LIBCPP___CXX03___ALGORITHM_MAKE_PROJECTED_H
0011
0012 #include <__cxx03/__concepts/same_as.h>
0013 #include <__cxx03/__config>
0014 #include <__cxx03/__functional/identity.h>
0015 #include <__cxx03/__functional/invoke.h>
0016 #include <__cxx03/__type_traits/decay.h>
0017 #include <__cxx03/__type_traits/enable_if.h>
0018 #include <__cxx03/__type_traits/integral_constant.h>
0019 #include <__cxx03/__type_traits/is_member_pointer.h>
0020 #include <__cxx03/__type_traits/is_same.h>
0021 #include <__cxx03/__utility/declval.h>
0022 #include <__cxx03/__utility/forward.h>
0023
0024 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0025 #  pragma GCC system_header
0026 #endif
0027
0028 _LIBCPP_BEGIN_NAMESPACE_STD
0029
0030 template <class _Pred, class _Proj>
0031 struct _ProjectedPred {
0032   _Pred& __pred; // Can be a unary or a binary predicate.
0033   _Proj& __proj;
0034
0035   _LIBCPP_CONSTEXPR _LIBCPP_HIDE_FROM_ABI _ProjectedPred(_Pred& __pred_arg, _Proj& __proj_arg)
0036       : __pred(__pred_arg), __proj(__proj_arg) {}
0037
0038   template <class _Tp>
0039   typename __invoke_of<_Pred&, decltype(std::__invoke(std::declval<_Proj&>(), std::declval<_Tp>()))>::type
0040       _LIBCPP_CONSTEXPR _LIBCPP_HIDE_FROM_ABI
0041       operator()(_Tp&& __v) const {
0042     return std::__invoke(__pred, std::__invoke(__proj, std::forward<_Tp>(__v)));
0043   }
0044
0045   template <class _T1, class _T2>
0046   typename __invoke_of<_Pred&,
0047                        decltype(std::__invoke(std::declval<_Proj&>(), std::declval<_T1>())),
0048                        decltype(std::__invoke(std::declval<_Proj&>(), std::declval<_T2>()))>::type _LIBCPP_CONSTEXPR
0049   _LIBCPP_HIDE_FROM_ABI
0050   operator()(_T1&& __lhs, _T2&& __rhs) const {
0051     return std::__invoke(
0052         __pred, std::__invoke(__proj, std::forward<_T1>(__lhs)), std::__invoke(__proj, std::forward<_T2>(__rhs)));
0053   }
0054 };
0055
0056 template <
0057     class _Pred,
0058     class _Proj,
0059     __enable_if_t<!(!is_member_pointer<__decay_t<_Pred> >::value && __is_identity<__decay_t<_Proj> >::value), int> = 0>
0060 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _ProjectedPred<_Pred, _Proj> __make_projected(_Pred& __pred, _Proj& __proj) {
0061   return _ProjectedPred<_Pred, _Proj>(__pred, __proj);
0062 }
0063
0064 // Avoid creating the functor and just use the pristine comparator -- for certain algorithms, this would enable
0065 // optimizations that rely on the type of the comparator. Additionally, this results in less layers of indirection in
0066 // the call stack when the comparator is invoked, even in an unoptimized build.
0067 template <
0068     class _Pred,
0069     class _Proj,
0070     __enable_if_t<!is_member_pointer<__decay_t<_Pred> >::value && __is_identity<__decay_t<_Proj> >::value, int> = 0>
0071 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _Pred& __make_projected(_Pred& __pred, _Proj&) {
0072   return __pred;
0073 }
0074
0075 _LIBCPP_END_NAMESPACE_STD
0076
0077 #if _LIBCPP_STD_VER >= 20
0078
0079 _LIBCPP_BEGIN_NAMESPACE_STD
0080
0081 namespace ranges {
0082
0083 template <class _Comp, class _Proj1, class _Proj2>
0084 _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) __make_projected_comp(_Comp& __comp, _Proj1& __proj1, _Proj2& __proj2) {
0085   if constexpr (__is_identity<decay_t<_Proj1>>::value && __is_identity<decay_t<_Proj2>>::value &&
0086                 !is_member_pointer_v<decay_t<_Comp>>) {
0087     // Avoid creating the lambda and just use the pristine comparator -- for certain algorithms, this would enable
0088     // optimizations that rely on the type of the comparator.
0089     return __comp;
0090
0091   } else {
0092     return [&](auto&& __lhs, auto&& __rhs) -> bool {
0093       return std::invoke(__comp,
0094                          std::invoke(__proj1, std::forward<decltype(__lhs)>(__lhs)),
0095                          std::invoke(__proj2, std::forward<decltype(__rhs)>(__rhs)));
0096     };
0097   }
0098 }
0099
0100 } // namespace ranges
0101
0102 _LIBCPP_END_NAMESPACE_STD
0103
0104 #endif // _LIBCPP_STD_VER >= 20
0105
0106 #endif // _LIBCPP___CXX03___ALGORITHM_MAKE_PROJECTED_H