mfbt/ReverseIterator.h
author Ryan VanderMeulen <ryanvm@gmail.com>
Thu, 24 May 2018 14:12:20 -0400
changeset 473436 0f95c023462e4de617ebdd77cbe90ec523efad10
parent 288304 02f08045a3bc004fcd2849fcaca05a220eee72c4
child 508163 6f3709b3878117466168c40affa7bca0b60cf75b
permissions -rw-r--r--
Backed out 5 changesets (bug 1462497) for causing widespread test failures. Backed out changeset f89eb2186154 (bug 1462497) Backed out changeset e8836b424826 (bug 1462497) Backed out changeset 3dcce8353e13 (bug 1462497) Backed out changeset 21f67c8e36fb (bug 1462497) Backed out changeset b14f835411db (bug 1462497)

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/* An iterator that acts like another iterator, but iterating in
 * the negative direction. (Note that not all iterators can iterate
 * in the negative direction.) */

#ifndef mozilla_ReverseIterator_h
#define mozilla_ReverseIterator_h

#include "mozilla/Attributes.h"
#include "mozilla/TypeTraits.h"

namespace mozilla {

template<typename IteratorT>
class ReverseIterator
{
public:
  template<typename Iterator>
  explicit ReverseIterator(Iterator aIter)
    : mCurrent(aIter) { }

  template<typename Iterator>
  MOZ_IMPLICIT ReverseIterator(const ReverseIterator<Iterator>& aOther)
    : mCurrent(aOther.mCurrent) { }

  decltype(*DeclVal<IteratorT>()) operator*() const
  {
    IteratorT tmp = mCurrent;
    return *--tmp;
  }

  /* Increments and decrements operators */

  ReverseIterator& operator++() { --mCurrent; return *this; }
  ReverseIterator& operator--() { ++mCurrent; return *this; }
  ReverseIterator operator++(int) { auto ret = *this; mCurrent--; return ret; }
  ReverseIterator operator--(int) { auto ret = *this; mCurrent++; return ret; }

  /* Comparison operators */

  template<typename Iterator1, typename Iterator2>
  friend bool operator==(const ReverseIterator<Iterator1>& aIter1,
                         const ReverseIterator<Iterator2>& aIter2);
  template<typename Iterator1, typename Iterator2>
  friend bool operator!=(const ReverseIterator<Iterator1>& aIter1,
                         const ReverseIterator<Iterator2>& aIter2);
  template<typename Iterator1, typename Iterator2>
  friend bool operator<(const ReverseIterator<Iterator1>& aIter1,
                        const ReverseIterator<Iterator2>& aIter2);
  template<typename Iterator1, typename Iterator2>
  friend bool operator<=(const ReverseIterator<Iterator1>& aIter1,
                         const ReverseIterator<Iterator2>& aIter2);
  template<typename Iterator1, typename Iterator2>
  friend bool operator>(const ReverseIterator<Iterator1>& aIter1,
                        const ReverseIterator<Iterator2>& aIter2);
  template<typename Iterator1, typename Iterator2>
  friend bool operator>=(const ReverseIterator<Iterator1>& aIter1,
                         const ReverseIterator<Iterator2>& aIter2);

private:
  IteratorT mCurrent;
};

template<typename Iterator1, typename Iterator2>
bool
operator==(const ReverseIterator<Iterator1>& aIter1,
           const ReverseIterator<Iterator2>& aIter2)
{
  return aIter1.mCurrent == aIter2.mCurrent;
}

template<typename Iterator1, typename Iterator2>
bool
operator!=(const ReverseIterator<Iterator1>& aIter1,
           const ReverseIterator<Iterator2>& aIter2)
{
  return aIter1.mCurrent != aIter2.mCurrent;
}

template<typename Iterator1, typename Iterator2>
bool
operator<(const ReverseIterator<Iterator1>& aIter1,
          const ReverseIterator<Iterator2>& aIter2)
{
  return aIter1.mCurrent > aIter2.mCurrent;
}

template<typename Iterator1, typename Iterator2>
bool
operator<=(const ReverseIterator<Iterator1>& aIter1,
           const ReverseIterator<Iterator2>& aIter2)
{
  return aIter1.mCurrent >= aIter2.mCurrent;
}

template<typename Iterator1, typename Iterator2>
bool
operator>(const ReverseIterator<Iterator1>& aIter1,
          const ReverseIterator<Iterator2>& aIter2)
{
  return aIter1.mCurrent < aIter2.mCurrent;
}

template<typename Iterator1, typename Iterator2>
bool
operator>=(const ReverseIterator<Iterator1>& aIter1,
           const ReverseIterator<Iterator2>& aIter2)
{
  return aIter1.mCurrent <= aIter2.mCurrent;
}

namespace detail {

template<typename IteratorT>
class IteratorRange
{
public:
  typedef IteratorT iterator;
  typedef IteratorT const_iterator;
  typedef ReverseIterator<IteratorT> reverse_iterator;
  typedef ReverseIterator<IteratorT> const_reverse_iterator;

  template<typename Iterator1, typename Iterator2>
  MOZ_IMPLICIT IteratorRange(Iterator1 aIterBegin, Iterator2 aIterEnd)
    : mIterBegin(aIterBegin), mIterEnd(aIterEnd) { }

  template<typename Iterator>
  MOZ_IMPLICIT IteratorRange(const IteratorRange<Iterator>& aOther)
    : mIterBegin(aOther.mIterBegin), mIterEnd(aOther.mIterEnd) { }

  iterator begin() const { return mIterBegin; }
  const_iterator cbegin() const { return begin(); }
  iterator end() const { return mIterEnd; }
  const_iterator cend() const { return end(); }
  reverse_iterator rbegin() const { return reverse_iterator(mIterEnd); }
  const_reverse_iterator crbegin() const { return rbegin(); }
  reverse_iterator rend() const { return reverse_iterator(mIterBegin); }
  const_reverse_iterator crend() const { return rend(); }

private:
  IteratorT mIterBegin;
  IteratorT mIterEnd;
};

} // namespace detail

template<typename Range>
detail::IteratorRange<typename Range::reverse_iterator>
Reversed(Range& aRange)
{
  return {aRange.rbegin(), aRange.rend()};
}

template<typename Range>
detail::IteratorRange<typename Range::const_reverse_iterator>
Reversed(const Range& aRange)
{
  return {aRange.rbegin(), aRange.rend()};
}

} // namespace mozilla

#endif // mozilla_ReverseIterator_h