libcxx/include/__algorithm/ranges_reverse.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_RANGES_REVERSE_H
  10 #define _LIBCPP___ALGORITHM_RANGES_REVERSE_H
  11
  12 #include <__config>
  13 #include <__iterator/concepts.h>
  14 #include <__iterator/iter_swap.h>
  15 #include <__iterator/next.h>
  16 #include <__iterator/permutable.h>
  17 #include <__ranges/access.h>
  18 #include <__ranges/concepts.h>
  19 #include <__ranges/dangling.h>
  20
  21 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  22 #  pragma GCC system_header
  23 #endif
  24
  25 #if _LIBCPP_STD_VER >= 20
  26
  27 _LIBCPP_BEGIN_NAMESPACE_STD
  28
  29 namespace ranges {
  30 struct __reverse {
  31   template <bidirectional_iterator _Iter, sentinel_for<_Iter> _Sent>
  32     requires permutable<_Iter>
  33   _LIBCPP_HIDE_FROM_ABI constexpr _Iter operator()(_Iter __first, _Sent __last) const {
  34     if constexpr (random_access_iterator<_Iter>) {
  35       if (__first == __last)
  36         return __first;
  37
  38       auto __end = ranges::next(__first, __last);
  39       auto __ret = __end;
  40
  41       while (__first < --__end) {
  42         ranges::iter_swap(__first, __end);
  43         ++__first;
  44       }
  45       return __ret;
  46     } else {
  47       auto __end = ranges::next(__first, __last);
  48       auto __ret = __end;
  49
  50       while (__first != __end) {
  51         if (__first == --__end)
  52           break;
  53
  54         ranges::iter_swap(__first, __end);
  55         ++__first;
  56       }
  57       return __ret;
  58     }
  59   }
  60
  61   template <bidirectional_range _Range>
  62     requires permutable<iterator_t<_Range>>
  63   _LIBCPP_HIDE_FROM_ABI constexpr borrowed_iterator_t<_Range> operator()(_Range&& __range) const {
  64     return (*this)(ranges::begin(__range), ranges::end(__range));
  65   }
  66 };
  67
  68 inline namespace __cpo {
  69 inline constexpr auto reverse = __reverse{};
  70 } // namespace __cpo
  71 } // namespace ranges
  72
  73 _LIBCPP_END_NAMESPACE_STD
  74
  75 #endif // _LIBCPP_STD_VER >= 20
  76
  77 #endif // _LIBCPP___ALGORITHM_RANGES_REVERSE_H