Add fromIterable(s) constructors in SplayTreeMap and LinkedHashMap.

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;
 
 /**
  * A hash-table based implementation of [Map].
  *
  * The keys of a `HashMap` 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.
  */
 class HashMap<K, V> implements Map<K, V> {
   external HashMap();
 
-  static _id(x) => x;
-
+  /**
+   * Creates a [HashMap] that contains all key value pairs of [other].
+   */
   factory HashMap.from(Map<K, V> other) {
     return new HashMap<K, V>()..addAll(other);
   }
 
-  factory HashMap.fromIterable(Iterable iterable,
+  /**
+   * Creates a [HashMap] 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 HashMap.fromIterable(Iterable<K> iterable,
       {K key(element), V value(element)}) {
     HashMap<K, V> map = new HashMap<K, V>();
-
-    if (key == null) key = _id;
-    if (value == null) value = _id;
-
-    for (var element in iterable) {
-      map[key(element)] = value(element);
-    }
-
+    Maps._fillMapWithMappedIterable(map, iterable, key, value);
     return map;
   }
 
+  /**
+   * Creates a [HashMap] 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 HashMap.fromIterables(Iterable<K> keys, Iterable<V> values) {
     HashMap<K, V> map = new HashMap<K, V>();
-
-    Iterator<K> keyIterator = keys.iterator;
-    Iterator<V> valueIterator = values.iterator;
-
-    bool hasNextKey = keyIterator.moveNext();
-    bool hasNextValue = valueIterator.moveNext();
-
-    while (hasNextKey && hasNextValue) {
-      map[keyIterator.current] = valueIterator.current;
-      hasNextKey = keyIterator.moveNext();
-      hasNextValue = valueIterator.moveNext();
-    }
-
-    if (hasNextKey || hasNextValue) {
-      throw new ArgumentError("Iterables do not have same length.");
-    }
-
+    Maps._fillMapWithIterables(map, keys, values);
     return map;
   }
 
   external int get length;
   external bool get isEmpty;
   external bool get isNotEmpty;
 
   external Iterable<K> get keys;
   external Iterable<V> get values;
 
   external bool containsKey(Object key);
   external bool containsValue(Object value);
 
   external void addAll(Map<K, V> other);
 
   external V operator [](Object key);
   external void operator []=(K key, V value);
 
   external V putIfAbsent(K key, V ifAbsent());
 
   external V remove(Object key);
   external void clear();
 
   external void forEach(void action(K key, V value));
 
   String toString() => Maps.mapToString(this);
 }