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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 part of dart.collection; | |
| 6 | |
| 7 /** Default function for equality comparison in customized HashMaps */ | |
| 8 bool _defaultEquals(Object a, Object b) => a == b; | |
| 9 /** Default function for hash-code computation in customized HashMaps */ | |
| 10 int _defaultHashCode(Object a) => a.hashCode; | |
| 11 | |
| 12 /** Type of custom equality function */ | |
| 13 typedef bool _Equality<K>(K a, K b); | |
| 14 /** Type of custom hash code function. */ | |
| 15 typedef int _Hasher<K>(K object); | |
| 16 | |
| 17 /** | |
| 18 * A hash-table based implementation of [Map]. | |
| 19 * | |
| 20 * The keys of a `HashMap` must have consistent [Object.operator==] | |
| 21 * and [Object.hashCode] implementations. This means that the `==` operator | |
| 22 * must define a stable equivalence relation on the keys (reflexive, | |
| 23 * symmetric, transitive, and consistent over time), and that `hashCode` | |
| 24 * must be the same for objects that are considered equal by `==`. | |
| 25 * | |
| 26 * The map allows `null` as a key. | |
| 27 * | |
| 28 * Iterating the map's keys, values or entries (through [forEach]) | |
| 29 * may happen in any order. | |
| 30 * The itearation order only changes when the map is modified. | |
| 31 * Values are iterated in the same order as their associated keys, | |
| 32 * so iterating the [keys] and [values] in parallel | |
| 33 * will give matching key and value pairs. | |
| 34 */ | |
| 35 abstract class HashMap<K, V> implements Map<K, V> { | |
| 36 /** | |
| 37 * Creates an unordered hash-table based [Map]. | |
| 38 * | |
| 39 * The created map is not ordered in any way. When iterating the keys or | |
| 40 * values, the iteration order is unspecified except that it will stay the | |
| 41 * same as long as the map isn't changed. | |
| 42 * | |
| 43 * If [equals] is provided, it is used to compare the keys in the table with | |
| 44 * new keys. If [equals] is omitted, the key's own [Object.operator==] is used | |
| 45 * instead. | |
| 46 * | |
| 47 * Similar, if [hashCode] is provided, it is used to produce a hash value | |
| 48 * for keys in order to place them in the hash table. If it is omitted, the | |
| 49 * key's own [Object.hashCode] is used. | |
| 50 * | |
| 51 * If using methods like [operator[]], [remove] and [containsKey] together | |
| 52 * with a custom equality and hashcode, an extra `isValidKey` function | |
| 53 * can be supplied. This function is called before calling [equals] or | |
| 54 * [hashCode] with an argument that may not be a [K] instance, and if the | |
| 55 * call returns false, the key is assumed to not be in the set. | |
| 56 * The [isValidKey] function defaults to just testing if the object is a | |
| 57 * [K] instance. | |
| 58 * | |
| 59 * The used `equals` and `hashCode` method should always be consistent, | |
| 60 * so that if `equals(a, b)` then `hashCode(a) == hashCode(b)`. The hash | |
| 61 * of an object, or what it compares equal to, should not change while the | |
| 62 * object is in the table. If it does change, the result is unpredictable. | |
| 63 * | |
| 64 * If you supply one of [equals] and [hashCode], | |
| 65 * you should generally also to supply the other. | |
| 66 * An example would be using [identical] and [identityHashCode], | |
| 67 * which is equivalent to using the shorthand [HashMap.identity]). | |
| 68 */ | |
| 69 factory HashMap({ bool equals(K key1, K key2), | |
| 70 int hashCode(K key), | |
| 71 bool isValidKey(Object potentialKey) }) { | |
| 72 if (isValidKey == null) { | |
| 73 if (hashCode == null) { | |
| 74 if (equals == null) { | |
| 75 return new _HashMap<K, V>(); | |
| 76 } | |
| 77 hashCode = _defaultHashCode; | |
| 78 } else { | |
| 79 if (identical(identityHashCode, hashCode) && | |
| 80 identical(identical, equals)) { | |
| 81 return new _IdentityHashMap<K, V>(); | |
| 82 } | |
| 83 if (equals == null) { | |
| 84 equals = _defaultEquals; | |
| 85 } | |
| 86 } | |
| 87 } else { | |
| 88 if (hashCode == null) { | |
| 89 hashCode = _defaultHashCode; | |
| 90 } | |
| 91 if (equals == null) { | |
| 92 equals = _defaultEquals; | |
| 93 } | |
| 94 } | |
| 95 return new _CustomHashMap<K, V>(equals, hashCode, isValidKey); | |
| 96 } | |
| 97 | |
| 98 /** | |
| 99 * Creates an unordered identity-based map. | |
| 100 * | |
| 101 * Effectively a shorthand for: | |
| 102 * | |
| 103 * new HashMap(equals: identical, hashCode: identityHashCodeOf) | |
| 104 */ | |
| 105 factory HashMap.identity() = _IdentityHashMap<K, V>; | |
| 106 | |
| 107 /** | |
| 108 * Creates a [HashMap] that contains all key/value pairs of [other]. | |
| 109 */ | |
| 110 factory HashMap.from(Map other) { | |
| 111 HashMap<K, V> result = new HashMap<K, V>(); | |
| 112 other.forEach((k, v) { result[k] = v; }); | |
| 113 return result; | |
| 114 } | |
| 115 | |
| 116 /** | |
| 117 * Creates a [HashMap] where the keys and values are computed from the | |
| 118 * [iterable]. | |
| 119 * | |
| 120 * For each element of the [iterable] this constructor computes a key/value | |
| 121 * pair, by applying [key] and [value] respectively. | |
| 122 * | |
| 123 * The keys of the key/value pairs do not need to be unique. The last | |
| 124 * occurrence of a key will simply overwrite any previous value. | |
| 125 * | |
| 126 * If no values are specified for [key] and [value] the default is the | |
| 127 * identity function. | |
| 128 */ | |
| 129 factory HashMap.fromIterable(Iterable iterable, | |
| 130 {K key(element), V value(element)}) { | |
| 131 HashMap<K, V> map = new HashMap<K, V>(); | |
| 132 Maps._fillMapWithMappedIterable(map, iterable, key, value); | |
| 133 return map; | |
| 134 } | |
| 135 | |
| 136 /** | |
| 137 * Creates a [HashMap] associating the given [keys] to [values]. | |
| 138 * | |
| 139 * This constructor iterates over [keys] and [values] and maps each element of | |
| 140 * [keys] to the corresponding element of [values]. | |
| 141 * | |
| 142 * If [keys] contains the same object multiple times, the last occurrence | |
| 143 * overwrites the previous value. | |
| 144 * | |
| 145 * It is an error if the two [Iterable]s don't have the same length. | |
| 146 */ | |
| 147 factory HashMap.fromIterables(Iterable<K> keys, Iterable<V> values) { | |
| 148 HashMap<K, V> map = new HashMap<K, V>(); | |
| 149 Maps._fillMapWithIterables(map, keys, values); | |
| 150 return map; | |
| 151 } | |
| 152 } | |
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