__cxx03/__iterator/prev.h

0001 // -*- C++ -*-
0002 //===----------------------------------------------------------------------===//
0003 //
0004 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
0005 // See https://llvm.org/LICENSE.txt for license information.
0006 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
0007 //
0008 //===----------------------------------------------------------------------===//
0009
0010 #ifndef _LIBCPP___CXX03___ITERATOR_PREV_H
0011 #define _LIBCPP___CXX03___ITERATOR_PREV_H
0012
0013 #include <__cxx03/__assert>
0014 #include <__cxx03/__config>
0015 #include <__cxx03/__iterator/advance.h>
0016 #include <__cxx03/__iterator/concepts.h>
0017 #include <__cxx03/__iterator/incrementable_traits.h>
0018 #include <__cxx03/__iterator/iterator_traits.h>
0019 #include <__cxx03/__type_traits/enable_if.h>
0020
0021 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0022 #  pragma GCC system_header
0023 #endif
0024
0025 _LIBCPP_BEGIN_NAMESPACE_STD
0026
0027 template <class _InputIter, __enable_if_t<__has_input_iterator_category<_InputIter>::value, int> = 0>
0028 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 _InputIter
0029 prev(_InputIter __x, typename iterator_traits<_InputIter>::difference_type __n = 1) {
0030   // Calling `advance` with a negative value on a non-bidirectional iterator is a no-op in the current implementation.
0031   // Note that this check duplicates the similar check in `std::advance`.
0032   _LIBCPP_ASSERT_PEDANTIC(__n <= 0 || __has_bidirectional_iterator_category<_InputIter>::value,
0033                           "Attempt to prev(it, n) with a positive n on a non-bidirectional iterator");
0034   std::advance(__x, -__n);
0035   return __x;
0036 }
0037
0038 #if _LIBCPP_STD_VER >= 20
0039
0040 // [range.iter.op.prev]
0041
0042 namespace ranges {
0043 namespace __prev {
0044
0045 struct __fn {
0046   template <bidirectional_iterator _Ip>
0047   _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x) const {
0048     --__x;
0049     return __x;
0050   }
0051
0052   template <bidirectional_iterator _Ip>
0053   _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n) const {
0054     ranges::advance(__x, -__n);
0055     return __x;
0056   }
0057
0058   template <bidirectional_iterator _Ip>
0059   _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n, _Ip __bound_iter) const {
0060     ranges::advance(__x, -__n, __bound_iter);
0061     return __x;
0062   }
0063 };
0064
0065 } // namespace __prev
0066
0067 inline namespace __cpo {
0068 inline constexpr auto prev = __prev::__fn{};
0069 } // namespace __cpo
0070 } // namespace ranges
0071
0072 #endif // _LIBCPP_STD_VER >= 20
0073
0074 _LIBCPP_END_NAMESPACE_STD
0075
0076 #endif // _LIBCPP___CXX03___ITERATOR_PREV_H