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1 // Copyright (c) 2013, 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 /** | |
6 * Contains functions that are included by default in [PolymerExpressions]. | |
7 * | |
8 * - [enumerate]: a convenient way to iterate over items and the indexes. | |
9 */ | |
10 // Code from https://github.com/google/quiver-dart/commit/52edc4baf37e99ff6a8f99
c648b29b135fc0b880 | |
11 library polymer_expressions.src.globals; | |
12 | |
13 import 'dart:collection'; | |
14 import 'package:observe/observe.dart' show reflectable; | |
15 | |
16 /** | |
17 * Returns an [Iterable] of [IndexedValue]s where the nth value holds the nth | |
18 * element of [iterable] and its index. | |
19 */ | |
20 Iterable<IndexedValue> enumerate(Iterable iterable) => | |
21 new EnumerateIterable(iterable); | |
22 | |
23 @reflectable class IndexedValue<V> { | |
24 final int index; | |
25 final V value; | |
26 | |
27 operator==(o) => o is IndexedValue && o.index == index && o.value == value; | |
28 int get hashCode => value.hashCode; | |
29 String toString() => '($index, $value)'; | |
30 | |
31 IndexedValue(this.index, this.value); | |
32 } | |
33 | |
34 /** | |
35 * An [Iterable] of [IndexedValue]s where the nth value holds the nth | |
36 * element of [iterable] and its index. See [enumerate]. | |
37 */ | |
38 // This was inspired by MappedIterable internal to Dart collections. | |
39 class EnumerateIterable<V> extends IterableBase<IndexedValue<V>> { | |
40 final Iterable<V> _iterable; | |
41 | |
42 EnumerateIterable(this._iterable); | |
43 | |
44 Iterator<IndexedValue<V>> get iterator => | |
45 new EnumerateIterator<V>(_iterable.iterator); | |
46 | |
47 // Length related functions are independent of the mapping. | |
48 int get length => _iterable.length; | |
49 bool get isEmpty => _iterable.isEmpty; | |
50 | |
51 // Index based lookup can be done before transforming. | |
52 IndexedValue<V> get first => new IndexedValue<V>(0, _iterable.first); | |
53 IndexedValue<V> get last => new IndexedValue<V>(length - 1, _iterable.last); | |
54 IndexedValue<V> get single => new IndexedValue<V>(0, _iterable.single); | |
55 IndexedValue<V> elementAt(int index) => | |
56 new IndexedValue<V>(index, _iterable.elementAt(index)); | |
57 } | |
58 | |
59 /** The [Iterator] returned by [EnumerateIterable.iterator]. */ | |
60 class EnumerateIterator<V> extends Iterator<IndexedValue<V>> { | |
61 final Iterator<V> _iterator; | |
62 int _index = 0; | |
63 IndexedValue<V> _current; | |
64 | |
65 EnumerateIterator(this._iterator); | |
66 | |
67 IndexedValue<V> get current => _current; | |
68 | |
69 bool moveNext() { | |
70 if (_iterator.moveNext()) { | |
71 _current = new IndexedValue(_index++, _iterator.current); | |
72 return true; | |
73 } | |
74 _current = null; | |
75 return false; | |
76 } | |
77 } | |
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