mfbt/ReverseIterator.h
author Dustin J. Mitchell <dustin@mozilla.com>
Wed, 07 Sep 2016 00:10:51 +0000
changeset 354971 1627fd341fc154d4fb771366676b7101204362df
parent 286645 02f08045a3bc004fcd2849fcaca05a220eee72c4
child 505383 6f3709b3878117466168c40affa7bca0b60cf75b
permissions -rw-r--r--
Bug 1286075: allow optimization of tasks whose dependencies have not been optimized; r=armenzg MikeLing initially did this in bug 1287018. The intent of this conditional was to make optimization faster by not even checking most tasks, based on the assumption that if the prerequisite to a task has changed (for example, a docker image or a build), then naturally we will want to execute that task. However, as we have developed actual optimization methods, this has proven not to be the case: we might want to optimize a test out if its inputs have not changed, even if a new installer has been built. Similarly, SETA may optimize tasks out even if their inputs have changed. MozReview-Commit-ID: LgHET3Z84GB

/* -*- 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