Make Iterable more powerful (and lazy).

sdk/lib/core/iterator.dart

 // Copyright (c) 2012, 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 [Iterator] class provides methods to iterate over an object. It
  * is transparently used by the for-in construct to test for the end
  * of the iteration, and to get the elements.
  *
  * If the object iterated over is changed during the iteration, the
  * behavior is unspecified.
+ *
+ * The [Iterator] is initially positioned before the first element. Before
+ * accessing the first element the iterator must thus be advanced ([moveNext])
+ * to point to the first element. If there is no element left, then [moveNext]
+ * returns false.
  */
 abstract class Iterator<E> {
   /**
-   * Gets the next element in the iteration. Throws a
-   * [StateError] if no element is left.
+   * Moves to the next element. Returns true if [current] contains the next
+   * element. Returns false, if no element was left. It the latter case
+   * trying to read [current] will throw a [StateError].
+   *
+   * It is safe to invoke [moveNext] even when the iterator is already
+   * positioned after the last element. In this case [moveNext] has no effect.
    */
-  E next();
+  bool moveNext();
 
   /**
-   * Returns whether the [Iterator] has elements left.
+   * Returns the current element.
+   *
+   * Throws a [StateError] if the iterator has not yet been moved to the first
+   * element, or if the iterator has been moved after the last element of the
+   * [Iterable].
    */
   bool hasNext;

[Lasse Reichstein Nielsen, 2012/11/12 09:38:03]

Change to 'T get current'?

[floitsch, 2012/11/16 22:31:07]

Done.

 }