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1 // Copyright (c) 2012, the Dart project authors. Please see the AUTHORS file | 1 // Copyright (c) 2012, the Dart project authors. Please see the AUTHORS file |
2 // for details. All rights reserved. Use of this source code is governed by a | 2 // for details. All rights reserved. Use of this source code is governed by a |
3 // BSD-style license that can be found in the LICENSE file. | 3 // BSD-style license that can be found in the LICENSE file. |
4 | 4 |
5 part of dart.core; | 5 part of dart.core; |
6 | 6 |
7 /** | 7 /** |
8 * An interface for getting items, one at a time, from an object. | 8 * An interface for getting items, one at a time, from an object. |
9 * | 9 * |
10 * The for-in construct transparently uses Iterator to test for the end | 10 * The for-in construct transparently uses `Iterator` to test for the end |
11 * of the iteration, and to get each item (or _element_). | 11 * of the iteration, and to get each item (or _element_). |
12 * | 12 * |
13 * If the object iterated over is changed during the iteration, the | 13 * If the object iterated over is changed during the iteration, the |
14 * behavior is unspecified. | 14 * behavior is unspecified. |
15 * | 15 * |
16 * The Iterator is initially positioned before the first element. Before | 16 * The `Iterator` is initially positioned before the first element. |
17 * accessing the first element the iterator must thus be advanced ([moveNext]) | 17 * Before accessing the first element the iterator must thus be advanced using |
18 * to point to the first element. If no element is left, then [moveNext] | 18 * [moveNext] to point to the first element. |
19 * returns false. | 19 * If no element is left, then [moveNext] returns false, [current] |
| 20 * returns `null`, and all further calls to [moveNext] will also return false. |
20 * | 21 * |
21 * A typical usage of an Iterator looks as follows: | 22 * A typical usage of an Iterator looks as follows: |
22 * | 23 * |
23 * var it = obj.iterator; | 24 * var it = obj.iterator; |
24 * while (it.moveNext()) { | 25 * while (it.moveNext()) { |
25 * use(it.current); | 26 * use(it.current); |
26 * } | 27 * } |
27 * | 28 * |
28 * **See also:** [Iteration] | 29 * **See also:** |
29 * (http://www.dartlang.org/docs/dart-up-and-running/contents/ch03.html#ch03-ite
ration) | 30 * [Iteration](http://www.dartlang.org/docs/dart-up-and-running/contents/ch03.ht
ml#iteration) |
30 * in the [library tour] | 31 * in the [library tour](http://www.dartlang.org/docs/dart-up-and-running/conten
ts/ch03.html) |
31 * (http://www.dartlang.org/docs/dart-up-and-running/contents/ch03.html) | |
32 */ | 32 */ |
33 abstract class Iterator<E> { | 33 abstract class Iterator<E> { |
34 /** | 34 /** |
35 * Moves to the next element. Returns true if [current] contains the next | 35 * Moves to the next element. |
36 * element. Returns false, if no element was left. | 36 * |
| 37 * Returns true if [current] contains the next element. |
| 38 * Returns false if no elements are left. |
37 * | 39 * |
38 * It is safe to invoke [moveNext] even when the iterator is already | 40 * It is safe to invoke [moveNext] even when the iterator is already |
39 * positioned after the last element. In this case [moveNext] has no effect. | 41 * positioned after the last element. |
| 42 * In this case [moveNext] returns false again and has no effect. |
| 43 * |
| 44 * A call to `moveNext` may throw if iteration has been broken by |
| 45 * changing the underlying collection. |
40 */ | 46 */ |
41 bool moveNext(); | 47 bool moveNext(); |
42 | 48 |
43 /** | 49 /** |
44 * Returns the current element. | 50 * Returns the current element. |
45 * | 51 * |
46 * Return [:null:] if the iterator has not yet been moved to the first | 52 * Returns `null` if the iterator has not yet been moved to the first |
47 * element, or if the iterator has been moved after the last element of the | 53 * element, or if the iterator has been moved past the last element of the |
48 * [Iterable]. | 54 * [Iterable]. |
| 55 * |
| 56 * The `current` getter should keep its value until the next call to |
| 57 * [moveNext], even if an underlying collection changes. |
| 58 * After a successful call to `moveNext`, the user doesn't need to cache |
| 59 * the current value, but can keep reading it from the iterator. |
49 */ | 60 */ |
50 E get current; | 61 E get current; |
51 } | 62 } |
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