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 <__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_header 23 #endif 24 25 _LIBCPP_PUSH_MACROS 26 #include <__undef_macros> 27 28 _LIBCPP_BEGIN_NAMESPACE_STD 29 30 template <class _InputIter, __enable_if_t<__has_input_iterator_category<_InputIter>::value, int> = 0> 31 [[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 _InputIter 32 prev(_InputIter __x, typename iterator_traits<_InputIter>::difference_type __n) { 33 std::advance(__x, -__n); 34 return __x; 35 } 36 37 // LWG 3197 38 // 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. 40 template <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 >= 20 48 49 // [range.iter.op.prev] 50 51 namespace ranges { 52 struct __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 _Ip 67 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 73 inline namespace __cpo { 74 inline constexpr auto prev = __prev{}; 75 } // namespace __cpo 76 } // namespace ranges 77 78 #endif // _LIBCPP_STD_VER >= 20 79 80 _LIBCPP_END_NAMESPACE_STD 81 82 _LIBCPP_POP_MACROS 83 84 #endif // _LIBCPP___ITERATOR_PREV_H 85