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 #include <__utility/move.h> 21 22 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 23 # pragma GCC system_header 24 #endif 25 26 _LIBCPP_PUSH_MACROS 27 #include <__undef_macros> 28 29 _LIBCPP_BEGIN_NAMESPACE_STD 30 31 template <class _InputIter, __enable_if_t<__has_input_iterator_category<_InputIter>::value, int> = 0> 32 [[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 _InputIter 33 prev(_InputIter __x, typename iterator_traits<_InputIter>::difference_type __n) { 34 // Calling `advance` with a negative value on a non-bidirectional iterator is a no-op in the current implementation. 35 // Note that this check duplicates the similar check in `std::advance`. 36 _LIBCPP_ASSERT_PEDANTIC(__n <= 0 || __has_bidirectional_iterator_category<_InputIter>::value, 37 "Attempt to prev(it, n) with a positive n on a non-bidirectional iterator"); 38 std::advance(__x, -__n); 39 return __x; 40 } 41 42 // LWG 3197 43 // It is unclear what the implications of "BidirectionalIterator" in the standard are. 44 // However, calling std::prev(non-bidi-iterator) is obviously an error and we should catch it at compile time. 45 template <class _InputIter, __enable_if_t<__has_input_iterator_category<_InputIter>::value, int> = 0> 46 [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 _InputIter prev(_InputIter __it) { 47 static_assert(__has_bidirectional_iterator_category<_InputIter>::value, 48 "Attempt to prev(it) with a non-bidirectional iterator"); 49 return std::prev(std::move(__it), 1); 50 } 51 52 #if _LIBCPP_STD_VER >= 20 53 54 // [range.iter.op.prev] 55 56 namespace ranges { 57 struct __prev { 58 template <bidirectional_iterator _Ip> 59 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x) const { 60 --__x; 61 return __x; 62 } 63 64 template <bidirectional_iterator _Ip> 65 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n) const { 66 ranges::advance(__x, -__n); 67 return __x; 68 } 69 70 template <bidirectional_iterator _Ip> 71 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Ip 72 operator()(_Ip __x, iter_difference_t<_Ip> __n, _Ip __bound_iter) const { 73 ranges::advance(__x, -__n, __bound_iter); 74 return __x; 75 } 76 }; 77 78 inline namespace __cpo { 79 inline constexpr auto prev = __prev{}; 80 } // namespace __cpo 81 } // namespace ranges 82 83 #endif // _LIBCPP_STD_VER >= 20 84 85 _LIBCPP_END_NAMESPACE_STD 86 87 _LIBCPP_POP_MACROS 88 89 #endif // _LIBCPP___ITERATOR_PREV_H 90