mfbt/ReverseIterator.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /* An iterator that acts like another iterator, but iterating in
   8  * the negative direction. (Note that not all iterators can iterate
   9  * in the negative direction.) */
  10
  11 #ifndef mozilla_ReverseIterator_h
  12 #define mozilla_ReverseIterator_h
  13
  14 #include <utility>
  15
  16 #include "mozilla/Attributes.h"
  17
  18 namespace mozilla {
  19
  20 template <typename IteratorT>
  21 class ReverseIterator {
  22  public:
  23   template <typename Iterator>
  24   explicit ReverseIterator(Iterator aIter) : mCurrent(aIter) {}
  25
  26   template <typename Iterator>
  27   MOZ_IMPLICIT ReverseIterator(const ReverseIterator<Iterator>& aOther)
  28       : mCurrent(aOther.mCurrent) {}
  29
  30   decltype(*std::declval<IteratorT>()) operator*() const {
  31     IteratorT tmp = mCurrent;
  32     return *--tmp;
  33   }
  34
  35   /* Increments and decrements operators */
  36
  37   ReverseIterator& operator++() {
  38     --mCurrent;
  39     return *this;
  40   }
  41   ReverseIterator& operator--() {
  42     ++mCurrent;
  43     return *this;
  44   }
  45   ReverseIterator operator++(int) {
  46     auto ret = *this;
  47     mCurrent--;
  48     return ret;
  49   }
  50   ReverseIterator operator--(int) {
  51     auto ret = *this;
  52     mCurrent++;
  53     return ret;
  54   }
  55
  56   /* Comparison operators */
  57
  58   template <typename Iterator1, typename Iterator2>
  59   friend bool operator==(const ReverseIterator<Iterator1>& aIter1,
  60                          const ReverseIterator<Iterator2>& aIter2);
  61   template <typename Iterator1, typename Iterator2>
  62   friend bool operator!=(const ReverseIterator<Iterator1>& aIter1,
  63                          const ReverseIterator<Iterator2>& aIter2);
  64   template <typename Iterator1, typename Iterator2>
  65   friend bool operator<(const ReverseIterator<Iterator1>& aIter1,
  66                         const ReverseIterator<Iterator2>& aIter2);
  67   template <typename Iterator1, typename Iterator2>
  68   friend bool operator<=(const ReverseIterator<Iterator1>& aIter1,
  69                          const ReverseIterator<Iterator2>& aIter2);
  70   template <typename Iterator1, typename Iterator2>
  71   friend bool operator>(const ReverseIterator<Iterator1>& aIter1,
  72                         const ReverseIterator<Iterator2>& aIter2);
  73   template <typename Iterator1, typename Iterator2>
  74   friend bool operator>=(const ReverseIterator<Iterator1>& aIter1,
  75                          const ReverseIterator<Iterator2>& aIter2);
  76
  77  private:
  78   IteratorT mCurrent;
  79 };
  80
  81 template <typename Iterator1, typename Iterator2>
  82 bool operator==(const ReverseIterator<Iterator1>& aIter1,
  83                 const ReverseIterator<Iterator2>& aIter2) {
  84   return aIter1.mCurrent == aIter2.mCurrent;
  85 }
  86
  87 template <typename Iterator1, typename Iterator2>
  88 bool operator!=(const ReverseIterator<Iterator1>& aIter1,
  89                 const ReverseIterator<Iterator2>& aIter2) {
  90   return aIter1.mCurrent != aIter2.mCurrent;
  91 }
  92
  93 template <typename Iterator1, typename Iterator2>
  94 bool operator<(const ReverseIterator<Iterator1>& aIter1,
  95                const ReverseIterator<Iterator2>& aIter2) {
  96   return aIter1.mCurrent > aIter2.mCurrent;
  97 }
  98
  99 template <typename Iterator1, typename Iterator2>
 100 bool operator<=(const ReverseIterator<Iterator1>& aIter1,
 101                 const ReverseIterator<Iterator2>& aIter2) {
 102   return aIter1.mCurrent >= aIter2.mCurrent;
 103 }
 104
 105 template <typename Iterator1, typename Iterator2>
 106 bool operator>(const ReverseIterator<Iterator1>& aIter1,
 107                const ReverseIterator<Iterator2>& aIter2) {
 108   return aIter1.mCurrent < aIter2.mCurrent;
 109 }
 110
 111 template <typename Iterator1, typename Iterator2>
 112 bool operator>=(const ReverseIterator<Iterator1>& aIter1,
 113                 const ReverseIterator<Iterator2>& aIter2) {
 114   return aIter1.mCurrent <= aIter2.mCurrent;
 115 }
 116
 117 namespace detail {
 118
 119 template <typename IteratorT>
 120 class IteratorRange {
 121  public:
 122   typedef IteratorT iterator;
 123   typedef IteratorT const_iterator;
 124   typedef ReverseIterator<IteratorT> reverse_iterator;
 125   typedef ReverseIterator<IteratorT> const_reverse_iterator;
 126
 127   template <typename Iterator1, typename Iterator2>
 128   MOZ_IMPLICIT IteratorRange(Iterator1 aIterBegin, Iterator2 aIterEnd)
 129       : mIterBegin(aIterBegin), mIterEnd(aIterEnd) {}
 130
 131   template <typename Iterator>
 132   MOZ_IMPLICIT IteratorRange(const IteratorRange<Iterator>& aOther)
 133       : mIterBegin(aOther.mIterBegin), mIterEnd(aOther.mIterEnd) {}
 134
 135   iterator begin() const { return mIterBegin; }
 136   const_iterator cbegin() const { return begin(); }
 137   iterator end() const { return mIterEnd; }
 138   const_iterator cend() const { return end(); }
 139   reverse_iterator rbegin() const { return reverse_iterator(mIterEnd); }
 140   const_reverse_iterator crbegin() const { return rbegin(); }
 141   reverse_iterator rend() const { return reverse_iterator(mIterBegin); }
 142   const_reverse_iterator crend() const { return rend(); }
 143
 144  private:
 145   IteratorT mIterBegin;
 146   IteratorT mIterEnd;
 147 };
 148
 149 }  // namespace detail
 150
 151 template <typename Range>
 152 detail::IteratorRange<typename Range::reverse_iterator> Reversed(
 153     Range& aRange) {
 154   return {aRange.rbegin(), aRange.rend()};
 155 }
 156
 157 template <typename Range>
 158 detail::IteratorRange<typename Range::const_reverse_iterator> Reversed(
 159     const Range& aRange) {
 160   return {aRange.rbegin(), aRange.rend()};
 161 }
 162
 163 }  // namespace mozilla
 164
 165 #endif  // mozilla_ReverseIterator_h