Add Map constructors taking iterables.

sdk/lib/core/map.dart

 // Copyright (c) 2011, 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.core;
 
 /**
  * A [Map] is an associative container, mapping a key to a value.
  * Null values are supported, but null keys are not.
  */
 abstract class Map<K, V> {
   /**
    * Creates a map with the default implementation.
    */
   factory Map() => new HashMap<K, V>();
 
   /**
    * Creates a [Map] that contains all key value pairs of [other].
    */
   factory Map.from(Map<K, V> other) => new HashMap<K, V>.from(other);
 
   /**
+   * Creates a map where each key is an element from [keys] with

[floitsch, 2013/06/27 11:45:04]

Try a shorter first sentence. More details in the next paragraph.

Creates a [Map] 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 ...

[zarah, 2013/06/27 13:02:43]

Done.

+   * its associated value being the element from [values] at the same position.
+   *
+   * The length of [keys] and [values] must be the same, otherwise an ArgumentError

[floitsch, 2013/06/27 11:45:04]

long line.

We usually don't say what kind of error happens:

"It is an error if the two [Iterable]s don't have the same length".

[zarah, 2013/06/27 13:02:43]

Done.

+   * is thrown.
+   */
+  factory Map.fromIterables(Iterable<K> keys, Iterable<V> values)
+      = HashMap<K, V>.fromIterables;
+
+  /**
+   * Creates a map where each key-value pair is computed from each element in

[floitsch, 2013/06/27 11:45:04]

Creates a [Map] where the keys and values are computed from the [iterable].
// new line to have a separate paragraph in the doc.
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 ...

[zarah, 2013/06/27 13:02:43]

Done.

+   * [iterable]. The key is computed by applying the [key] function to the
+   * element and the value is computed by applying the [value] function to the
+   * same element.
+   *
+   * If no values are specified for [key] and [value] the default is the
+   * identity function.
+   */
+  factory Map.fromIterable(Iterable iterable,
+      {K key(element), V value(element)}) = HashMap<K, V>.fromIterable;
+
+  /**
    * Returns whether this map contains the given [value].
    */
   bool containsValue(Object value);
 
   /**
    * Returns whether this map contains the given [key].
    */
   bool containsKey(Object key);
 
   /**
@@ skipping 68 matching lines @@
   /**
    * Returns true if there is no {key, value} pair in the map.
    */
   bool get isEmpty;
 
   /**
    * Returns true if there is at least one {key, value} pair in the map.
    */
   bool get isNotEmpty;
 }