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/* -*- 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 */
// Common iterator implementation for array classes e.g. nsTArray.
#ifndef mozilla_ArrayIterator_h
#define mozilla_ArrayIterator_h
#include <iterator>
#include <type_traits>
namespace mozilla {
namespace detail {
template <typename T>
struct AddInnerConst;
template <typename T>
struct AddInnerConst<T&> {
using Type = const T&;
template <typename T>
struct AddInnerConst<T*> {
using Type = const T*;
template <typename T>
using AddInnerConstT = typename AddInnerConst<T>::Type;
} // namespace detail
// We have implemented a custom iterator class for array rather than using
// raw pointers into the backing storage to improve the safety of C++11-style
// range based iteration in the presence of array mutation, or script execution
// (bug 1299489).
// Mutating an array which is being iterated is still wrong, and will either
// cause elements to be missed or firefox to crash, but will not trigger memory
// safety problems due to the release-mode bounds checking found in ElementAt.
// Dereferencing this iterator returns type Element. When Element is a reference
// type, this iterator implements the full standard random access iterator spec,
// and can be treated in many ways as though it is a pointer. Otherwise, it is
// just enough to be used in range-based for loop.
template <class Element, class ArrayType>
class ArrayIterator {
typedef ArrayType array_type;
typedef ArrayIterator<Element, ArrayType> iterator_type;
typedef typename array_type::index_type index_type;
typedef std::remove_reference_t<Element> value_type;
typedef ptrdiff_t difference_type;
typedef value_type* pointer;
typedef value_type& reference;
typedef std::random_access_iterator_tag iterator_category;
typedef ArrayIterator<detail::AddInnerConstT<Element>, ArrayType>
const array_type* mArray;
index_type mIndex;
ArrayIterator() : mArray(nullptr), mIndex(0) {}
ArrayIterator(const iterator_type& aOther)
: mArray(aOther.mArray), mIndex(aOther.mIndex) {}
ArrayIterator(const array_type& aArray, index_type aIndex)
: mArray(&aArray), mIndex(aIndex) {}
iterator_type& operator=(const iterator_type& aOther) {
mArray = aOther.mArray;
mIndex = aOther.mIndex;
return *this;
constexpr operator const_iterator_type() const {
return mArray ? const_iterator_type{*mArray, mIndex}
: const_iterator_type{};
bool operator==(const iterator_type& aRhs) const {
return mIndex == aRhs.mIndex;
bool operator!=(const iterator_type& aRhs) const { return !(*this == aRhs); }
bool operator<(const iterator_type& aRhs) const {
return mIndex < aRhs.mIndex;
bool operator>(const iterator_type& aRhs) const {
return mIndex > aRhs.mIndex;
bool operator<=(const iterator_type& aRhs) const {
return mIndex <= aRhs.mIndex;
bool operator>=(const iterator_type& aRhs) const {
return mIndex >= aRhs.mIndex;
// These operators depend on the release mode bounds checks in
// ArrayIterator::ElementAt for safety.
value_type* operator->() const {
return const_cast<value_type*>(&mArray->ElementAt(mIndex));
Element operator*() const {
return const_cast<Element>(mArray->ElementAt(mIndex));
iterator_type& operator++() {
return *this;
iterator_type operator++(int) {
iterator_type it = *this;
return it;
iterator_type& operator--() {
return *this;
iterator_type operator--(int) {
iterator_type it = *this;
return it;
iterator_type& operator+=(difference_type aDiff) {
mIndex += aDiff;
return *this;
iterator_type& operator-=(difference_type aDiff) {
mIndex -= aDiff;
return *this;
iterator_type operator+(difference_type aDiff) const {
iterator_type it = *this;
it += aDiff;
return it;
iterator_type operator-(difference_type aDiff) const {
iterator_type it = *this;
it -= aDiff;
return it;
difference_type operator-(const iterator_type& aOther) const {
return static_cast<difference_type>(mIndex) -
Element operator[](difference_type aIndex) const {
return *this->operator+(aIndex);
constexpr const array_type* GetArray() const { return mArray; }
constexpr index_type GetIndex() const { return mIndex; }
} // namespace mozilla
#endif // mozilla_ArrayIterator_h