libcxx/include/__iterator/prev.h

   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 // [range.iter.op.prev]
  41
  42 namespace ranges {
  43 namespace __prev {
  44
  45 struct __fn final : private __function_like {
  46   _LIBCPP_HIDE_FROM_ABI
  47   constexpr explicit __fn(__tag __x) noexcept : __function_like(__x) {}
  48
  49   template <bidirectional_iterator _Ip>
  50   _LIBCPP_HIDE_FROM_ABI
  51   constexpr _Ip operator()(_Ip __x) const {
  52     --__x;
  53     return __x;
  54   }
  55
  56   template <bidirectional_iterator _Ip>
  57   _LIBCPP_HIDE_FROM_ABI
  58   constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n) const {
  59     ranges::advance(__x, -__n);
  60     return __x;
  61   }
  62
  63   template <bidirectional_iterator _Ip>
  64   _LIBCPP_HIDE_FROM_ABI
  65   constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n, _Ip __bound) const {
  66     ranges::advance(__x, -__n, __bound);
  67     return __x;
  68   }
  69 };
  70
  71 } // namespace __prev
  72
  73 inline namespace __cpo {
  74   inline constexpr auto prev = __prev::__fn(__function_like::__tag());
  75 } // namespace __cpo
  76 } // namespace ranges
  77
  78 #endif // !defined(_LIBCPP_HAS_NO_RANGES)
  79
  80 _LIBCPP_END_NAMESPACE_STD
  81
  82 #endif // _LIBCPP___ITERATOR_PREV_H