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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 | |
3 // BSD-style license that can be found in the LICENSE file. | |
4 | |
5 part of dart.collection; | |
6 | |
7 /** | |
8 * The [HasNextIterator] class wraps an [Iterator] and provides methods to | |
9 * iterate over an object using `hasNext` and `next`. | |
10 * | |
11 * An [HasNextIterator] does not implement the [Iterator] interface. | |
12 */ | |
13 class HasNextIterator<E> { | |
14 static const int _HAS_NEXT_AND_NEXT_IN_CURRENT = 0; | |
15 static const int _NO_NEXT = 1; | |
16 static const int _NOT_MOVED_YET = 2; | |
17 | |
18 Iterator<E> _iterator; | |
19 int _state = _NOT_MOVED_YET; | |
20 | |
21 HasNextIterator(this._iterator); | |
22 | |
23 bool get hasNext { | |
24 if (_state == _NOT_MOVED_YET) _move(); | |
25 return _state == _HAS_NEXT_AND_NEXT_IN_CURRENT; | |
26 } | |
27 | |
28 E next() { | |
29 // Call to hasNext is necessary to make sure we are positioned at the first | |
30 // element when we start iterating. | |
31 if (!hasNext) throw new StateError("No more elements"); | |
32 assert(_state == _HAS_NEXT_AND_NEXT_IN_CURRENT); | |
33 E result = _iterator.current; | |
34 _move(); | |
35 return result; | |
36 } | |
37 | |
38 void _move() { | |
39 if (_iterator.moveNext()) { | |
40 _state = _HAS_NEXT_AND_NEXT_IN_CURRENT; | |
41 } else { | |
42 _state = _NO_NEXT; | |
43 } | |
44 } | |
45 } | |
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