content: // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
  // for details. All rights reserved. Use of this source code is governed by a
  // BSD-style license that can be found in the LICENSE file.
  
  part of dart.collection;
  
  /**
   * A hash-table based implementation of [Map].
   *
   * Keys insertion order is remembered, and keys are iterated in insertion order.
   * Values are iterated in their corresponding key's order.
   *
   * The keys of a `LinkedHashMap` must have consistent [Object.operator==]
   * and [Object.hashCode] implementations. This means that the `==` operator
   * must define a stable equivalence relation on the keys (reflexive,
   * anti-symmetric, transitive, and consistent over time), and that `hashCode`
   * must be the same for objects that are considered equal by `==`.
   *
   * The map allows `null` as a key.
   */
  abstract class LinkedHashMap<K, V> implements HashMap<K, V> {
    external factory LinkedHashMap({ bool equals(K key1, K key2),
                                     int hashCode(K key),
                                     bool isValidKey(potentialKey) });
  
    /**
     * Creates an insertion-ordered identity-based map.
     *
     * Effectively a shorthand for:
     *
     *     new LinkedHashMap(equals: identical, hashCode: identityHashCodeOf)
     */
    external factory LinkedHashMap.identity();
  
    /**
     * Creates a [LinkedHashMap] that contains all key value pairs of [other].
     */
    factory LinkedHashMap.from(Map<K, V> other) {
      return new LinkedHashMap<K, V>()..addAll(other);
    }
  
    /**
     * Creates a [LinkedHashMap] where the keys and values are computed from the
     * [iterable].
     *
     * For each element of the [iterable] this constructor computes a key/value
     * pair, by applying [key] and [value] respectively.
     *
     * The keys of the key/value pairs do not need to be unique. The last
     * occurrence of a key will simply overwrite any previous value.
     *
     * If no values are specified for [key] and [value] the default is the
     * identity function.
     */
    factory LinkedHashMap.fromIterable(Iterable iterable,
        {K key(element), V value(element)}) {
      LinkedHashMap<K, V> map = new LinkedHashMap<K, V>();
      Maps._fillMapWithMappedIterable(map, iterable, key, value);
      return map;
    }
  
    /**
     * Creates a [LinkedHashMap] associating the given [keys] to [values].
     *
     * This constructor iterates over [keys] and [values] and maps each element of
     * [keys] to the corresponding element of [values].
     *
     * If [keys] contains the same object multiple times, the last occurrence
     * overwrites the previous value.
     *
     * It is an error if the two [Iterable]s don't have the same length.
     */
    factory LinkedHashMap.fromIterables(Iterable<K> keys, Iterable<V> values) {
      LinkedHashMap<K, V> map = new LinkedHashMap<K, V>();
      Maps._fillMapWithIterables(map, keys, values);
      return map;
    }
  }
  