85 lines · c
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-exception7//8//===----------------------------------------------------------------------===//9 10#ifndef _LIBCPP___ITERATOR_PREV_H11#define _LIBCPP___ITERATOR_PREV_H12 13#include <__config>14#include <__iterator/advance.h>15#include <__iterator/concepts.h>16#include <__iterator/incrementable_traits.h>17#include <__iterator/iterator_traits.h>18#include <__type_traits/enable_if.h>19#include <__utility/move.h>20 21#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)22# pragma GCC system_header23#endif24 25_LIBCPP_PUSH_MACROS26#include <__undef_macros>27 28_LIBCPP_BEGIN_NAMESPACE_STD29 30template <class _InputIter, __enable_if_t<__has_input_iterator_category<_InputIter>::value, int> = 0>31[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 _InputIter32prev(_InputIter __x, typename iterator_traits<_InputIter>::difference_type __n) {33 std::advance(__x, -__n);34 return __x;35}36 37// LWG 319738// It is unclear what the implications of "BidirectionalIterator" in the standard are.39// However, calling std::prev(non-bidi-iterator) is obviously an error and we should catch it at compile time.40template <class _InputIter, __enable_if_t<__has_input_iterator_category<_InputIter>::value, int> = 0>41[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 _InputIter prev(_InputIter __it) {42 static_assert(__has_bidirectional_iterator_category<_InputIter>::value,43 "Attempt to prev(it) with a non-bidirectional iterator");44 return std::prev(std::move(__it), 1);45}46 47#if _LIBCPP_STD_VER >= 2048 49// [range.iter.op.prev]50 51namespace ranges {52struct __prev {53 template <bidirectional_iterator _Ip>54 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x) const {55 --__x;56 return __x;57 }58 59 template <bidirectional_iterator _Ip>60 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n) const {61 ranges::advance(__x, -__n);62 return __x;63 }64 65 template <bidirectional_iterator _Ip>66 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Ip67 operator()(_Ip __x, iter_difference_t<_Ip> __n, _Ip __bound_iter) const {68 ranges::advance(__x, -__n, __bound_iter);69 return __x;70 }71};72 73inline namespace __cpo {74inline constexpr auto prev = __prev{};75} // namespace __cpo76} // namespace ranges77 78#endif // _LIBCPP_STD_VER >= 2079 80_LIBCPP_END_NAMESPACE_STD81 82_LIBCPP_POP_MACROS83 84#endif // _LIBCPP___ITERATOR_PREV_H85