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> 28 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX17 29 typename enable_if<__is_cpp17_input_iterator<_InputIter>::value, _InputIter>::type 30 prev(_InputIter __x, typename iterator_traits<_InputIter>::difference_type __n = 1) { 31 _LIBCPP_ASSERT(__n <= 0 || __is_cpp17_bidirectional_iterator<_InputIter>::value, 32 "Attempt to prev(it, n) with a positive n on a non-bidirectional iterator"); 33 _VSTD::advance(__x, -__n); 34 return __x; 35 } 36 37 #if _LIBCPP_STD_VER > 17 38 39 // [range.iter.op.prev] 40 41 namespace ranges { 42 namespace __prev { 43 44 struct __fn { 45 template <bidirectional_iterator _Ip> 46 _LIBCPP_HIDE_FROM_ABI 47 constexpr _Ip operator()(_Ip __x) const { 48 --__x; 49 return __x; 50 } 51 52 template <bidirectional_iterator _Ip> 53 _LIBCPP_HIDE_FROM_ABI 54 constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n) const { 55 ranges::advance(__x, -__n); 56 return __x; 57 } 58 59 template <bidirectional_iterator _Ip> 60 _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n, _Ip __bound_iter) const { 61 ranges::advance(__x, -__n, __bound_iter); 62 return __x; 63 } 64 }; 65 66 } // namespace __prev 67 68 inline namespace __cpo { 69 inline constexpr auto prev = __prev::__fn{}; 70 } // namespace __cpo 71 } // namespace ranges 72 73 #endif // _LIBCPP_STD_VER > 17 74 75 _LIBCPP_END_NAMESPACE_STD 76 77 #endif // _LIBCPP___ITERATOR_PREV_H 78