Implement Map.unmodifiable

tool/input_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;
 
 /**
  * An collection of key-value pairs, from which you retrieve a value
  * using its associated key.
  *
@@ skipping 33 matching lines @@
    * The keys must all be assignable to [K] and the values to [V].
    * The [other] map itself can have any type.
    *
    * A `LinkedHashMap` requires the keys to implement compatible
    * `operator==` and `hashCode`, and it allows null as a key.
    * It iterates in key insertion order.
    */
   factory Map.from(Map other) = LinkedHashMap<K, V>.from;
 
   /**
+   * Creates an unmodifiable hash based map containing the entries of [other].
+   *
+   * The keys must all be assignable to [K] and the values to [V].
+   * The [other] map itself can have any type.
+   *
+   * The map requires the keys to implement compatible
+   * `operator==` and `hashCode`, and it allows `null` as a key.
+   * The created map iterates keys in a fixed order,
+   * preserving the order provided by [other].
+   *
+   * The resulting map behaves like the result of [Map.from],
+   * except that the map returned by this constructor is not modifiable.
+   */
+  external factory Map.unmodifiable(Map other);
+
+  /**
    * Creates an identity map with the default implementation, [LinkedHashMap].
    *
    * The returned map allows `null` as a key.
    * It iterates in key insertion order.
    */
   factory Map.identity() = LinkedHashMap<K, V>.identity;
 
   /**
    * Creates a Map instance in which the keys and values are computed from the
    * [iterable].
@@ skipping 62 matching lines @@
    * Returns true if this map contains the given [value].
    *
    * Returns true if any of the values in the map are equal to `value`
    * according to the `==` operator.
    */
   bool containsValue(Object value);
 
   /**
    * Returns true if this map contains the given [key].
    *
-   * Returns true if any of the keys in the map ar equal to `key`
+   * Returns true if any of the keys in the map are equal to `key`
    * according to the equality used by the map.
    */
   bool containsKey(Object key);
 
   /**
    * Returns the value for the given [key] or null if [key] is not in the map.
    *
    * Some maps allows keys to have `null` as a value,
    * For those maps, a lookup using this operator does cannot be used to
    * distinguish between a key not being in the map, and the key having a null
@@ skipping 98 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;
 }