| // 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.==] |
| * and [Object.hashCode] implementations. This means that the `==` operator |
| * must define a stable equivalence relation on the keys (reflexive, |
| * 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. |
| * |
| * Iterating the map's keys, values or entries (through [forEach]) |
| * may happen in any order. |
| * The iteration order only changes when the map is modified. |
| * Values are iterated in the same order as their associated keys, |
| * so iterating the [keys] and [values] in parallel |
| * will give matching key and value pairs. |
| */ |
| abstract class HashMap<K, V> implements Map<K, V> { |
| /** |
| * Creates an unordered 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.==] 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. |
| * |
| * Example: |
| * |
| * new HashMap<int,int>(equals: (int a, int b) => (b - a) % 5 == 0, |
| * hashCode: (int e) => e % 5) |
| * |
| * This example map does not need an `isValidKey` function to be passed. |
| * The default function accepts only `int` values, which can safely be |
| * passed to both the `equals` and `hashCode` functions. |
| * |
| * If neither `equals`, `hashCode`, nor `isValidKey` is provided, |
| * the default `isValidKey` instead accepts all keys. |
| * The default equality and hashcode operations are assumed to work on all |
| * objects. |
| * |
| * Likewise, if `equals` is [identical], `hashCode` is [identityHashCode] |
| * and `isValidKey` is omitted, the resulting map is identity based, |
| * and the `isValidKey` defaults to accepting all keys. |
| * Such a map can be created directly using [HashMap.identity]. |
| * |
| * 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 a key in the map. If it does change, the result is unpredictable. |
| * |
| * If you supply one of [equals] and [hashCode], |
| * you should generally also to supply the other. |
| */ |
| 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<K, V>(equals: identical, |
| * hashCode: identityHashCode) |
| */ |
| external factory HashMap.identity(); |
| |
| /** |
| * Creates a [HashMap] that contains all key/value pairs of [other]. |
| * |
| * The keys must all be instances of [K] and the values of [V]. |
| * The [other] map itself can have any type. |
| */ |
| factory HashMap.from(Map other) { |
| Map<K, V> result = new HashMap<K, V>(); |
| other.forEach((k, v) { |
| result[k] = v; |
| }); |
| return result; |
| } |
| |
| /** |
| * Creates a [HashMap] that contains all key/value pairs of [other]. |
| */ |
| factory HashMap.of(Map<K, V> other) => 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)}) { |
| Map<K, V> map = new HashMap<K, V>(); |
| MapBase._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) { |
| Map<K, V> map = new HashMap<K, V>(); |
| MapBase._fillMapWithIterables(map, keys, values); |
| return map; |
| } |
| |
| /** |
| * Creates a [HashMap] containing the entries of [entries]. |
| * |
| * Returns a new `HashMap<K, V>` where all entries of [entries] |
| * have been added in iteration order. |
| * |
| * If multiple [entries] have the same key, |
| * later occurrences overwrite the earlier ones. |
| */ |
| @Since("2.1") |
| factory HashMap.fromEntries(Iterable<MapEntry<K, V>> entries) => |
| HashMap<K, V>()..addEntries(entries); |
| } |