gecko-dev/xpcom/string/nsStringIterator.h

/* -*- 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/. */

#ifndef nsStringIterator_h___
#define nsStringIterator_h___

#include "nsCharTraits.h"
#include "nsAlgorithm.h"
#include "nsDebug.h"

/**
 * @see nsTAString
 */

template <class CharT>
class nsReadingIterator {
 public:
  typedef nsReadingIterator<CharT> self_type;
  typedef ptrdiff_t difference_type;
  typedef size_t size_type;
  typedef CharT value_type;
  typedef const CharT* pointer;
  typedef const CharT& reference;

 private:
  friend class mozilla::detail::nsTStringRepr<CharT>;

  // unfortunately, the API for nsReadingIterator requires that the
  // iterator know its start and end positions.  this was needed when
  // we supported multi-fragment strings, but now it is really just
  // extra baggage.  we should remove mStart and mEnd at some point.

  const CharT* mStart;
  const CharT* mEnd;
  const CharT* mPosition;

 public:
  nsReadingIterator() : mStart(nullptr), mEnd(nullptr), mPosition(nullptr) {}
  // clang-format off
  // nsReadingIterator( const nsReadingIterator<CharT>& );                    // auto-generated copy-constructor OK
  // nsReadingIterator<CharT>& operator=( const nsReadingIterator<CharT>& );  // auto-generated copy-assignment operator OK
  // clang-format on

  pointer get() const { return mPosition; }

  CharT operator*() const { return *get(); }

  self_type& operator++() {
    ++mPosition;
    return *this;
  }

  self_type operator++(int) {
    self_type result(*this);
    ++mPosition;
    return result;
  }

  self_type& operator--() {
    --mPosition;
    return *this;
  }

  self_type operator--(int) {
    self_type result(*this);
    --mPosition;
    return result;
  }

  self_type& advance(difference_type aN) {
    if (aN > 0) {
      difference_type step = XPCOM_MIN(aN, mEnd - mPosition);

      NS_ASSERTION(
          step > 0,
          "can't advance a reading iterator beyond the end of a string");

      mPosition += step;
    } else if (aN < 0) {
      difference_type step = XPCOM_MAX(aN, -(mPosition - mStart));

      NS_ASSERTION(step < 0,
                   "can't advance (backward) a reading iterator beyond the end "
                   "of a string");

      mPosition += step;
    }
    return *this;
  }

  // We return an unsigned type here (with corresponding assert) rather than
  // the more usual difference_type because we want to make this class go
  // away in favor of mozilla::RangedPtr.  Since RangedPtr has the same
  // requirement we are enforcing here, the transition ought to be much
  // smoother.
  size_type operator-(const self_type& aOther) const {
    MOZ_ASSERT(mPosition >= aOther.mPosition);
    return mPosition - aOther.mPosition;
  }
};

template <class CharT>
inline bool operator==(const nsReadingIterator<CharT>& aLhs,
                       const nsReadingIterator<CharT>& aRhs) {
  return aLhs.get() == aRhs.get();
}

template <class CharT>
inline bool operator!=(const nsReadingIterator<CharT>& aLhs,
                       const nsReadingIterator<CharT>& aRhs) {
  return aLhs.get() != aRhs.get();
}

#endif /* !defined(nsStringIterator_h___) */