libcxx/include/__iterator/prev.h

   1 // -*- C++ -*-
   2 //===----------------------------------------------------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #ifndef _LIBCPP___ITERATOR_PREV_H
  11 #define _LIBCPP___ITERATOR_PREV_H
  12
  13 #include <__assert>
  14 #include <__config>
  15 #include <__iterator/advance.h>
  16 #include <__iterator/concepts.h>
  17 #include <__iterator/incrementable_traits.h>
  18 #include <__iterator/iterator_traits.h>
  19 #include <__type_traits/enable_if.h>
  20
  21 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  22 #  pragma GCC system_header
  23 #endif
  24
  25 _LIBCPP_BEGIN_NAMESPACE_STD
  26
  27 template <class _InputIter, __enable_if_t<__has_input_iterator_category<_InputIter>::value, int> = 0>
  28 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX17
  29     _InputIter
  30     prev(_InputIter __x, typename iterator_traits<_InputIter>::difference_type __n = 1) {
  31   _LIBCPP_ASSERT_UNCATEGORIZED(__n <= 0 || __has_bidirectional_iterator_category<_InputIter>::value,
  32                                "Attempt to prev(it, n) with a positive n on a non-bidirectional iterator");
  33   _VSTD::advance(__x, -__n);
  34   return __x;
  35 }
  36
  37 #if _LIBCPP_STD_VER >= 20
  38
  39 // [range.iter.op.prev]
  40
  41 namespace ranges {
  42 namespace __prev {
  43
  44 struct __fn {
  45   template <bidirectional_iterator _Ip>
  46   _LIBCPP_HIDE_FROM_ABI
  47   constexpr _Ip operator()(_Ip __x) const {
  48     --__x;
  49     return __x;
  50   }
  51
  52   template <bidirectional_iterator _Ip>
  53   _LIBCPP_HIDE_FROM_ABI
  54   constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n) const {
  55     ranges::advance(__x, -__n);
  56     return __x;
  57   }
  58
  59   template <bidirectional_iterator _Ip>
  60   _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n, _Ip __bound_iter) const {
  61     ranges::advance(__x, -__n, __bound_iter);
  62     return __x;
  63   }
  64 };
  65
  66 } // namespace __prev
  67
  68 inline namespace __cpo {
  69   inline constexpr auto prev = __prev::__fn{};
  70 } // namespace __cpo
  71 } // namespace ranges
  72
  73 #endif // _LIBCPP_STD_VER >= 20
  74
  75 _LIBCPP_END_NAMESPACE_STD
  76
  77 #endif // _LIBCPP___ITERATOR_PREV_H