| // Copyright (c) 2013, 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.collection; |
| |
| /** Default function for equality comparison in customized HashMaps */ |
| bool _defaultEquals(a, b) => a == b; |
| /** Default function for hash-code computation in customized HashMaps */ |
| int _defaultHashCode(a) => a.hashCode; |
| |
| /** Type of custom equality function */ |
| typedef bool _Equality<K>(K a, K b); |
| /** Type of custom hash code function. */ |
| typedef int _Hasher<K>(K object); |
| |
| /** |
| * A hash-table based implementation of [Map]. |
| * |
| * The keys of a `HashMap` must have consistent [Object.operator==] |
| * and [Object.hashCode] implementations. This means that the `==` operator |
| * must define a stable equivalence relation on the keys (reflexive, |
| * anti-symmetric, transitive, and consistent over time), and that `hashCode` |
| * must be the same for objects that are considered equal by `==`. |
| * |
| * The map allows `null` as a key. |
| */ |
| abstract class HashMap<K, V> implements Map<K, V> { |
| /** |
| * Creates a hash-table based [Map]. |
| * |
| * The created map is not ordered in any way. When iterating the keys or |
| * values, the iteration order is unspecified except that it will stay the |
| * same as long as the map isn't changed. |
| * |
| * If [equals] is provided, it is used to compare the keys in the table with |
| * new keys. If [equals] is omitted, the key's own [Object.operator==] is used |
| * instead. |
| * |
| * Similar, if [hashCode] is provided, it is used to produce a hash value |
| * for keys in order to place them in the hash table. If it is omitted, the |
| * key's own [Object.hashCode] is used. |
| * |
| * If using methods like [operator[]], [remove] and [containsKey] together |
| * with a custom equality and hashcode, an extra `isValidKey` function |
| * can be supplied. This function is called before calling [equals] or |
| * [hashCode] with an argument that may not be a [K] instance, and if the |
| * call returns false, the key is assumed to not be in the set. |
| * The [isValidKey] function defaults to just testing if the object is a |
| * [K] instance. |
| * |
| * The used `equals` and `hashCode` method should always be consistent, |
| * so that if `equals(a, b)` then `hashCode(a) == hashCode(b)`. The hash |
| * of an object, or what it compares equal to, should not change while the |
| * object is in the table. If it does change, the result is unpredictable. |
| * |
| * It is generally the case that if you supply one of [equals] and [hashCode], |
| * you also want to supply the other. The only common exception is to pass |
| * [identical] as the equality and use the default hash code. |
| */ |
| external factory HashMap({bool equals(K key1, K key2), |
| int hashCode(K key), |
| bool isValidKey(potentialKey)}); |
| |
| /** |
| * Creates an unordered identity-based map. |
| * |
| * Effectively a shorthand for: |
| * |
| * new HashMap(equals: identical, hashCode: identityHashCodeOf) |
| */ |
| external factory HashMap.identity(); |
| |
| /** |
| * Creates a [HashMap] that contains all key value pairs of [other]. |
| */ |
| factory HashMap.from(Map<K, V> other) { |
| return new HashMap<K, V>()..addAll(other); |
| } |
| |
| /** |
| * Creates a [HashMap] where the keys and values are computed from the |
| * [iterable]. |
| * |
| * For each element of the [iterable] this constructor computes a key/value |
| * pair, by applying [key] and [value] respectively. |
| * |
| * The keys of the key/value pairs do not need to be unique. The last |
| * occurrence of a key will simply overwrite any previous value. |
| * |
| * If no values are specified for [key] and [value] the default is the |
| * identity function. |
| */ |
| factory HashMap.fromIterable(Iterable iterable, |
| {K key(element), V value(element)}) { |
| HashMap<K, V> map = new HashMap<K, V>(); |
| Maps._fillMapWithMappedIterable(map, iterable, key, value); |
| return map; |
| } |
| |
| /** |
| * Creates a [HashMap] associating the given [keys] to [values]. |
| * |
| * This constructor iterates over [keys] and [values] and maps each element of |
| * [keys] to the corresponding element of [values]. |
| * |
| * If [keys] contains the same object multiple times, the last occurrence |
| * overwrites the previous value. |
| * |
| * It is an error if the two [Iterable]s don't have the same length. |
| */ |
| factory HashMap.fromIterables(Iterable<K> keys, Iterable<V> values) { |
| HashMap<K, V> map = new HashMap<K, V>(); |
| Maps._fillMapWithIterables(map, keys, values); |
| return map; |
| } |
| } |