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// 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,
* and all further calls to [moveNext] will also return false.
* The [current] value must not be accessed before calling [moveNext]
* or after a call to [moveNext] has returned false.
* A typical usage of an Iterator looks as follows:
* var it = obj.iterator;
* while (it.moveNext()) {
* use(it.current);
* }
* **See also:**
* [Iteration](
* in the [library tour](
abstract class Iterator<E> {
* Advances the iterator to the next element of the iteration.
* Should be called before reading [current].
* If the call to `moveNext` returns `true`,
* then [current] will contain the next element of the iteration
* until `moveNext` is called again.
* If the call returns `false`, there are no further elements
* and [current] should not be used any more.
* It is safe to call [moveNext] after it has already returned `false`,
* but it must keep returning `false` and not have any other effect.
* A call to `moveNext` may throw for various reasons,
* including a concurrent change to an underlying collection.
* If that happens, the iterator may be in an inconsistent
* state, and any further behavior of the iterator is unspecified,
* including the effect of reading [current].
bool moveNext();
* Returns the current element.
* If the iterator has not yet been moved to the first element
* ([moveNext] has not been called yet),
* or if the iterator has been moved past the last element of the [Iterable]
* ([moveNext] has returned false),
* then [current] is unspecified.
* An [Iterator] may either throw or return an iterator specific default value
* in that case.
* 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;