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 _LIBCPP_ASSERT_UNCATEGORIZED(__n <= 0 || __has_bidirectional_iterator_category<_InputIter>::value, 31 "Attempt to prev(it, n) with a positive n on a non-bidirectional iterator"); 32 std::advance(__x, -__n); 33 return __x; 34 } 35 36 #if _LIBCPP_STD_VER >= 20 37 38 // [range.iter.op.prev] 39 40 namespace ranges { 41 namespace __prev { 42 43 struct __fn { 44 template <bidirectional_iterator _Ip> 45 _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x) const { 46 --__x; 47 return __x; 48 } 49 50 template <bidirectional_iterator _Ip> 51 _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n) const { 52 ranges::advance(__x, -__n); 53 return __x; 54 } 55 56 template <bidirectional_iterator _Ip> 57 _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n, _Ip __bound_iter) const { 58 ranges::advance(__x, -__n, __bound_iter); 59 return __x; 60 } 61 }; 62 63 } // namespace __prev 64 65 inline namespace __cpo { 66 inline constexpr auto prev = __prev::__fn{}; 67 } // namespace __cpo 68 } // namespace ranges 69 70 #endif // _LIBCPP_STD_VER >= 20 71 72 _LIBCPP_END_NAMESPACE_STD 73 74 #endif // _LIBCPP___ITERATOR_PREV_H 75