Extend Iterable instead of implementing it.

sdk/lib/core/iterable.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.
 
 /**
  * The [Iterable] interface allows to get an [Iterator] out of an
  * [Iterable] object.
  *
  * This interface is used by the for-in construct to iterate over an
  * [Iterable] object.
  * The for-in construct takes an [Iterable] object at the right-hand
  * side, and calls its [iterator] method to get an [Iterator] on it.
  *
  * A user-defined class that implements the [Iterable] interface can
  * be used as the right-hand side of a for-in construct.
  */
 abstract class Iterable<E> {
+  const Iterable();
+
   /**
    * Returns an [Iterator] that iterates over this [Iterable] object.
    */
   Iterator<E> iterator();
 
   /**
    * Returns a new collection with the elements [: f(e) :]
    * for each element [:e:] of this collection.
    *
    * Subclasses of [Collection] should implement the [mappedBy] method
    * to return a collection of the same general type as themselves.
    * E.g., [List.mappedBy] should return a [List].
    */
-  Collection mappedBy(f(E element));
+  Collection mappedBy(f(E element)) {
+    // TODO(floitsch): this is just a temporary function to provide a complete
+    // skeleton. It will be changed to become lazy soon.

[sra1, 2012/11/15 01:02:18]

How will it be lazy?

[floitsch, 2012/11/15 01:27:27]

Have a look here:
https://chromiumcodereview.appspot.com/11366111/

+    List result = new List();

[sra1, 2012/11/15 01:02:18]

Any reason to use new List() when the more concise [] means the same?

[floitsch, 2012/11/15 01:27:27]

Done.

+    for (E element in this) result.add(f(element));
+    return result;
+  }
 
   /**
    * Returns a collection with the elements of this collection
    * that satisfy the predicate [f].
    *
    * The returned collection should be of the same type as the collection
    * creating it.
    *
    * An element satisfies the predicate [f] if [:f(element):]
    * returns true.
    */
-  Collection<E> where(bool f(E element));
+  Collection<E> where(bool f(E element)) {
+    // TODO(floitsch): this is just a temporary function to provide a complete
+    // skeleton. It will be changed to become lazy soon.
+    List result = new List<E>();

[sra1, 2012/11/15 01:02:18]

Ditto <E>[]

[floitsch, 2012/11/15 01:27:27]

Done.

+    for (E element in this) if (f(element)) result.add(element);
+    return result;
+  }
 
   /**
    * Check whether the collection contains an element equal to [element].
    */
   bool contains(E element) {
     for (E e in this) {
       if (e == element) return true;
     }
     return false;
   }
 
   /**
    * Applies the function [f] to each element of this collection.
    */
   void forEach(void f(E element)) {
     for (E element in this) f(element);
   }
 
   /**
    * Reduce a collection to a single value by iteratively combining each element
    * of the collection with an existing value using the provided function.
    * Use [initialValue] as the initial value, and the function [combine] to
    * create a new value from the previous one and an element.
    *
    * Example of calculating the sum of a collection:
    *
    *   collection.reduce(0, (prev, element) => prev + element);
    */
   Dynamic reduce(var initialValue,

[sra1, 2012/11/15 01:02:18]

Dynamic -> dynamic ?

[floitsch, 2012/11/15 01:27:27]

Done.

                  Dynamic combine(var previousValue, E element)) {
     var value = initialValue;
     for (E element in this) value = combine(value, element);
     return value;
   }
 
   /**
    * Returns true if every elements of this collection satisify the
    * predicate [f]. Returns false otherwise.
    */
@@ skipping 13 matching lines @@
       if (f(element)) return true;
     }
     return false;
   }
 
   /**
    * Returns true if there is no element in this collection.
    */
   bool get isEmpty => !iterator().hasNext;
 }