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 27template <class _InputIter, __enable_if_t<__has_input_iterator_category<_InputIter>::value, int> = 0> 28inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 _InputIter 29prev(_InputIter __x, typename iterator_traits<_InputIter>::difference_type __n = 1) { 30 // Calling `advance` with a negative value on a non-bidirectional iterator is a no-op in the current implementation. 31 // Note that this check duplicates the similar check in `std::advance`. 32 _LIBCPP_ASSERT_PEDANTIC(__n <= 0 || __has_bidirectional_iterator_category<_InputIter>::value, 33 "Attempt to prev(it, n) with a positive n on a non-bidirectional iterator"); 34 std::advance(__x, -__n); 35 return __x; 36} 37 38#if _LIBCPP_STD_VER >= 20 39 40// [range.iter.op.prev] 41 42namespace ranges { 43namespace __prev { 44 45struct __fn { 46 template <bidirectional_iterator _Ip> 47 _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x) const { 48 --__x; 49 return __x; 50 } 51 52 template <bidirectional_iterator _Ip> 53 _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n) const { 54 ranges::advance(__x, -__n); 55 return __x; 56 } 57 58 template <bidirectional_iterator _Ip> 59 _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n, _Ip __bound_iter) const { 60 ranges::advance(__x, -__n, __bound_iter); 61 return __x; 62 } 63}; 64 65} // namespace __prev 66 67inline namespace __cpo { 68inline constexpr auto prev = __prev::__fn{}; 69} // namespace __cpo 70} // namespace ranges 71 72#endif // _LIBCPP_STD_VER >= 20 73 74_LIBCPP_END_NAMESPACE_STD 75 76#endif // _LIBCPP___ITERATOR_PREV_H 77