unfork DDC's copy of most SDK libraries

pkg/dev_compiler/tool/input_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.
-
-part of dart.core;
-
-/**
- * An interface for getting items, one at a time, from an object.
- *
- * The for-in construct transparently uses `Iterator` to test for the end
- * of the iteration, and to get each item (or _element_).
- *
- * 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 using
- * [moveNext] to point to the first element.
- * If no element is left, then [moveNext] returns false, [current]
- * returns `null`, and all further calls to [moveNext] will also return false.
- *
- * A typical usage of an Iterator looks as follows:
- *
- *     var it = obj.iterator;
- *     while (it.moveNext()) {
- *       use(it.current);
- *     }
- *
- * **See also:**
- * [Iteration](http://www.dartlang.org/docs/dart-up-and-running/contents/ch03.html#iteration)
- * in the [library tour](http://www.dartlang.org/docs/dart-up-and-running/contents/ch03.html)
- */
-abstract class Iterator<E> {
-  /**
-   * Moves to the next element.
-   *
-   * Returns true if [current] contains the next element.
-   * Returns false if no elements are left.
-   *
-   * It is safe to invoke [moveNext] even when the iterator is already
-   * positioned after the last element.
-   * In this case [moveNext] returns false again and has no effect.
-   *
-   * A call to `moveNext` may throw if iteration has been broken by
-   * changing the underlying collection.
-   */
-  bool moveNext();
-
-  /**
-   * Returns the current element.
-   *
-   * Returns `null` if the iterator has not yet been moved to the first
-   * element, or if the iterator has been moved past the last element of the
-   * [Iterable].
-   *
-   * The `current` getter should keep its value until the next call to
-   * [moveNext], even if an underlying collection changes.
-   * After a successful call to `moveNext`, the user doesn't need to cache
-   * the current value, but can keep reading it from the iterator.
-   */
-  E get current;
-}