Update {,Linked}Hash{Set,Map} documentation.

sdk/lib/collection/hash_map.dart

 // 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;
 
 /** Default function for equality comparison in customized HashMaps */
 bool _defaultEquals(a, b) => a == b;
 /** Default function for hash-code computation in customized HashMaps */
 int _defaultHashCode(a) => a.hashCode;
@@ skipping 38 matching lines @@
    * key's own [Object.hashCode] is used.
    *
    * If using methods like [operator[]], [remove] and [containsKey] together
    * with a custom equality and hashcode, an extra `isValidKey` function
    * can be supplied. This function is called before calling [equals] or
    * [hashCode] with an argument that may not be a [K] instance, and if the
    * call returns false, the key is assumed to not be in the set.
    * The [isValidKey] function defaults to just testing if the object is a
    * [K] instance.
    *
+   * Example:
+   *
+   *     new HashMap<int,int>(equals: (int a, int b) => (b - a) % 5 == 0,
+   *                          hashCode: (int e) => e % 5)
+   *
+   * This example map does not need an `isValidKey` function to be passed.
+   * The default function accepts only `int` values, which can safely be
+   * passed to both the `equals` and `hashCode` functions.
+   *
+   * If neither `equals`, `hashCode`, nor `isValidKey` is provided,
+   * the default `isValidKey` instead accepts all keys.
+   * The default equality and hashcode operations are assumed to work on all
+   * objects.
+   *
+   * Likewise, if `equals` is [identical], `hashCode` is [identityHashCode]
+   * and `isValidKey` is omitted, the resulting map is identity based,
+   * and the `isValidKey` defaults to accepting all keys.
+   * Such a map can be created directly using [HashMap.identity].
+   *
    * The used `equals` and `hashCode` method should always be consistent,
    * so that if `equals(a, b)` then `hashCode(a) == hashCode(b)`. The hash
    * of an object, or what it compares equal to, should not change while the
-   * object is in the table. If it does change, the result is unpredictable.
+   * object is a key in the map. If it does change, the result is unpredictable.
    *
    * If you supply one of [equals] and [hashCode],
    * you should generally also to supply the other.
-   * An example would be using [identical] and [identityHashCode],
-   * which is equivalent to using the shorthand [HashMap.identity]).
    */
   external factory HashMap({bool equals(K key1, K key2),
                             int hashCode(K key),
                             bool isValidKey(potentialKey)});
 
   /**
    * Creates an unordered identity-based map.
    *
    * Effectively a shorthand for:
    *
-   *     new HashMap(equals: identical, hashCode: identityHashCodeOf)
+   *     new HashMap(equals: identical,
+   *                 hashCode: identityHashCodeOf)
    */
   external factory HashMap.identity();
 
   /**
    * Creates a [HashMap] that contains all key/value pairs of [other].
    */
   factory HashMap.from(Map other) {
     HashMap<K, V> result = new HashMap<K, V>();
     other.forEach((k, v) { result[k] = v; });
     return result;
@@ skipping 29 matching lines @@
    * overwrites the previous value.
    *
    * It is an error if the two [Iterable]s don't have the same length.
    */
   factory HashMap.fromIterables(Iterable<K> keys, Iterable<V> values) {
     HashMap<K, V> map = new HashMap<K, V>();
     Maps._fillMapWithIterables(map, keys, values);
     return map;
   }
 }