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 [LinkedHashSet] is a hash-table based [Set] implementation.
   *
   * The `LinkedHashSet` also keep track of the order that elements were inserted
   * in, and iteration happens in first-to-last insertion order.
   *
   * The elements of a `LinkedHashSet` must have consistent [Object.operator==]
   * and [Object.hashCode] implementations. This means that the `==` operator
   * must define a stable equivalence relation on the elements (reflexive,
   * anti-symmetric, transitive, and consistent over time), and that `hashCode`
   * must be the same for objects that are considered equal by `==`.
   *
   * The set allows `null` as an element.
   *
   * Most simple operations on `HashSet` are done in (potentially amortized)
   * constant time: [add], [contains], [remove], and [length], provided the hash
   * codes of objects are well distributed..
   */
  abstract class LinkedHashSet<E> implements HashSet<E> {
  
    external factory LinkedHashSet({ bool equals(E e1, E e2),
                                     int hashCode(E e),
                                     bool isValidKey(potentialKey) });
  
    /**
     * Creates an insertion-ordered identity-based set.
     *
     * Effectively a shorthand for:
     *
     *     new LinkedHashSet(equals: identical, hashCode: identityHashCodeOf)
     */
    external factory LinkedHashSet.identity();
  
  
    factory LinkedHashSet.from(Iterable<E> iterable) {
      return new LinkedHashSet<E>()..addAll(iterable);
    }
  }
  