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 27 template <class _InputIter, __enable_if_t<__has_input_iterator_category<_InputIter>::value, int> = 0> 28 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 _InputIter 29 prev(_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 42 namespace ranges { 43 namespace __prev { 44 45 struct __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 67 inline namespace __cpo { 68 inline 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