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 <__debug>
15 #include <__function_like.h>
16 #include <__iterator/advance.h>
17 #include <__iterator/concepts.h>
18 #include <__iterator/incrementable_traits.h>
19 #include <__iterator/iterator_traits.h>
20 #include <type_traits>
21 
22 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
23 #pragma GCC system_header
24 #endif
25 
26 _LIBCPP_BEGIN_NAMESPACE_STD
27 
28 template <class _InputIter>
29 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
30     typename enable_if<__is_cpp17_input_iterator<_InputIter>::value, _InputIter>::type
31     prev(_InputIter __x, typename iterator_traits<_InputIter>::difference_type __n = 1) {
32   _LIBCPP_ASSERT(__n <= 0 || __is_cpp17_bidirectional_iterator<_InputIter>::value,
33                  "Attempt to prev(it, n) with a positive n on a non-bidirectional iterator");
34   _VSTD::advance(__x, -__n);
35   return __x;
36 }
37 
38 #if !defined(_LIBCPP_HAS_NO_RANGES)
39 
40 namespace ranges {
41 // TODO(varconst): rename `__prev_fn` to `__fn`.
42 struct __prev_fn final : private __function_like {
43   _LIBCPP_HIDE_FROM_ABI
44   constexpr explicit __prev_fn(__tag __x) noexcept : __function_like(__x) {}
45 
46   template <bidirectional_iterator _Ip>
47   _LIBCPP_HIDE_FROM_ABI
48   constexpr _Ip operator()(_Ip __x) const {
49     --__x;
50     return __x;
51   }
52 
53   template <bidirectional_iterator _Ip>
54   _LIBCPP_HIDE_FROM_ABI
55   constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n) const {
56     ranges::advance(__x, -__n);
57     return __x;
58   }
59 
60   template <bidirectional_iterator _Ip>
61   _LIBCPP_HIDE_FROM_ABI
62   constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n, _Ip __bound) const {
63     ranges::advance(__x, -__n, __bound);
64     return __x;
65   }
66 };
67 
68 inline constexpr auto prev = __prev_fn(__function_like::__tag());
69 } // namespace ranges
70 
71 #endif // !defined(_LIBCPP_HAS_NO_RANGES)
72 
73 _LIBCPP_END_NAMESPACE_STD
74 
75 #endif // _LIBCPP___ITERATOR_PREV_H
76