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+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+// This is a simplistic insertion-ordered map. It behaves similarly to an STL
+// map, but only implements a small subset of the map's methods. Internally, we
+// just keep a map and a list going in parallel.
+//
+// This class provides no thread safety guarantees, beyond what you would
+// normally see with std::list.
+//
+// Iterators should be stable in the face of mutations, except for an
+// iterator pointing to an element that was just deleted.
+
+#ifndef UTIL_GTL_LINKED_HASH_MAP_H_
+#define UTIL_GTL_LINKED_HASH_MAP_H_
+
+#include <list>
+#include <utility>
+
+#include "base/containers/hash_tables.h"
+#include "base/logging.h"
+
+// This holds a list of pair<Key, Value> items. This list is what gets
+// traversed, and it's iterators from this list that we return from
+// begin/end/find.
+//
+// We also keep a map<Key, list::iterator> for find. Since std::list is a
+// doubly-linked list, the iterators should remain stable.
+template<class Key, class Value>
+class linked_hash_map {
+ private:
+ typedef std::list<std::pair<Key, Value> > ListType;
+ typedef base::hash_map<Key, typename ListType::iterator> MapType;
+
+ public:
+ typedef typename ListType::iterator iterator;
+ typedef typename ListType::reverse_iterator reverse_iterator;
+ typedef typename ListType::const_iterator const_iterator;
+ typedef typename ListType::const_reverse_iterator const_reverse_iterator;
+ typedef typename MapType::key_type key_type;
+ typedef typename ListType::value_type value_type;
+ typedef typename ListType::size_type size_type;
+
+ linked_hash_map() : map_(), list_() {
+ }
+
+ // Returns an iterator to the first (insertion-ordered) element. Like a map,
+ // this can be dereferenced to a pair<Key, Value>.
+ iterator begin() {
+ return list_.begin();
+ }
+ const_iterator begin() const {
+ return list_.begin();
+ }
+
+ // Returns an iterator beyond the last element.
+ iterator end() {
+ return list_.end();
+ }
+ const_iterator end() const {
+ return list_.end();
+ }
+
+ // Returns an iterator to the last (insertion-ordered) element. Like a map,
+ // this can be dereferenced to a pair<Key, Value>.
+ reverse_iterator rbegin() {
+ return list_.rbegin();
+ }
+ const_reverse_iterator rbegin() const {
+ return list_.rbegin();
+ }
+
+ // Returns an iterator beyond the first element.
+ reverse_iterator rend() {
+ return list_.rend();
+ }
+ const_reverse_iterator rend() const {
+ return list_.rend();
+ }
+
+ // Clears the map of all values.
+ void clear() {
+ map_.clear();
+ list_.clear();
+ }
+
+ // Returns true iff the map is empty.
+ bool empty() const {
+ return list_.empty();
+ }
+
+ // Erases values with the provided key. Returns the number of elements
+ // erased. In this implementation, this will be 0 or 1.
+ size_type erase(const Key& key) {
+ typename MapType::iterator found = map_.find(key);
+ if (found == map_.end()) return 0;
+
+ list_.erase(found->second);
+ map_.erase(found);
+
+ return 1;
+ }
+
+ // Erases values with the provided iterator. If the provided iterator is
+ // invalid or there is inconsistency between the map and list, a CHECK() error
+ // will occur.
+ void erase(iterator position) {
+ typename MapType::iterator found = map_.find(position->first);
+ CHECK(found->second == position)
+ << "Inconsisent iterator for map and list, or the iterator is invalid.";
+
+ list_.erase(position);
+ map_.erase(found);
+ }
+
+ // Erases values between first and last, not including last.
+ void erase(iterator first, iterator last) {
+ while (first != last && first != end()) {
+ erase(first++);
+ }
+ }
+
+ // Finds the element with the given key. Returns an iterator to the
+ // value found, or to end() if the value was not found. Like a map, this
+ // iterator points to a pair<Key, Value>.
+ iterator find(const Key& key) {
+ typename MapType::iterator found = map_.find(key);
+ if (found == map_.end()) {
+ return end();
+ }
+ return found->second;
+ }
+
+ const_iterator find(const Key& key) const {
+ typename MapType::const_iterator found = map_.find(key);
+ if (found == map_.end()) {
+ return end();
+ }
+ return found->second;
+ }
+
+ // Returns the bounds of a range that includes all the elements in the
+ // container with a key that compares equal to x.
+ std::pair<iterator, iterator> equal_range(const key_type& key) {
+ std::pair<typename MapType::iterator, typename MapType::iterator> eq_range =
+ map_.equal_range(key);
+
+ return make_pair(eq_range.first->second, eq_range.second->second);
+ }
+
+ std::pair<const_iterator, const_iterator> equal_range(
+ const key_type& key) const {
+ std::pair<typename MapType::const_iterator,
+ typename MapType::const_iterator> eq_range =
+ map_.equal_range(key);
+ const const_iterator& start_iter = eq_range.first != map_.end() ?
+ eq_range.first->second : end();
+ const const_iterator& end_iter = eq_range.second != map_.end() ?
+ eq_range.second->second : end();
+
+ return make_pair(start_iter, end_iter);
+ }
+
+ // Returns the value mapped to key, or an inserted iterator to that position
+ // in the map.
+ Value& operator[](const key_type& key) {
+ return (*((this->insert(make_pair(key, Value()))).first)).second;
+ }
+
+ // Inserts an element into the map
+ std::pair<iterator, bool> insert(const std::pair<Key, Value>& pair) {
+ // First make sure the map doesn't have a key with this value. If it does,
+ // return a pair with an iterator to it, and false indicating that we
+ // didn't insert anything.
+ typename MapType::iterator found = map_.find(pair.first);
+ if (found != map_.end()) return make_pair(found->second, false);
+
+ // Otherwise, insert into the list first.
+ list_.push_back(pair);
+
+ // Obtain an iterator to the newly added element. We do -- instead of -
+ // since list::iterator doesn't implement operator-().
+ typename ListType::iterator last = list_.end();
+ --last;
+
+ CHECK(map_.insert(make_pair(pair.first, last)).second)
+ << "Map and list are inconsistent";
+
+ return make_pair(last, true);
+ }
+
+ size_type size() const {
+ return list_.size();
+ }
+
+ void swap(linked_hash_map& other) {
+ map_.swap(other.map_);
+ list_.swap(other.list_);
+ }
+
+ private:
+ // The map component, used for speedy lookups
+ MapType map_;
+
+ // The list component, used for maintaining insertion order
+ ListType list_;
+};
+
+#endif // UTIL_GTL_LINKED_HASH_MAP_H_