| // 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; |
| |
| /// A hash-table based implementation of [Map]. |
| /// |
| /// The insertion order of keys is remembered, |
| /// and keys are iterated in the order they were inserted into the map. |
| /// Values are iterated in their corresponding key's order. |
| /// Changing a key's value, when the key is already in the map, |
| /// does not change the iteration order, |
| /// but removing the key and adding it again |
| /// will make it be last in the iteration order. |
| /// |
| /// The keys of a `LinkedHashMap` 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 `==`. |
| abstract class LinkedHashMap<K, V> implements Map<K, V> { |
| /// Creates an insertion-ordered hash-table based [Map]. |
| /// |
| /// 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: |
| /// ```dart template:expression |
| /// LinkedHashMap<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 [LinkedHashMap.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 in the table. 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 LinkedHashMap( |
| {bool Function(K, K)? equals, |
| int Function(K)? hashCode, |
| bool Function(dynamic)? isValidKey}); |
| |
| /// Creates an insertion-ordered identity-based map. |
| /// |
| /// Effectively a shorthand for: |
| /// ```dart template:expression |
| /// LinkedHashMap<K, V>(equals: identical, |
| /// hashCode: identityHashCode) |
| /// ``` |
| external factory LinkedHashMap.identity(); |
| |
| /// Creates a [LinkedHashMap] that contains all key value pairs of [other]. |
| /// |
| /// The keys must all be instances of [K] and the values to [V]. |
| /// The [other] map itself can have any type. |
| factory LinkedHashMap.from(Map<dynamic, dynamic> other) { |
| LinkedHashMap<K, V> result = LinkedHashMap<K, V>(); |
| other.forEach((dynamic k, dynamic v) { |
| result[k as K] = v as V; |
| }); |
| return result; |
| } |
| |
| /// Creates a [LinkedHashMap] that contains all key value pairs of [other]. |
| factory LinkedHashMap.of(Map<K, V> other) => |
| LinkedHashMap<K, V>()..addAll(other); |
| |
| /// Creates a [LinkedHashMap] 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 LinkedHashMap.fromIterable(Iterable iterable, |
| {K Function(dynamic element)? key, V Function(dynamic element)? value}) { |
| LinkedHashMap<K, V> map = LinkedHashMap<K, V>(); |
| MapBase._fillMapWithMappedIterable(map, iterable, key, value); |
| return map; |
| } |
| |
| /// Creates a [LinkedHashMap] 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 LinkedHashMap.fromIterables(Iterable<K> keys, Iterable<V> values) { |
| LinkedHashMap<K, V> map = LinkedHashMap<K, V>(); |
| MapBase._fillMapWithIterables(map, keys, values); |
| return map; |
| } |
| |
| /// Creates a [LinkedHashMap] containing the entries of [entries]. |
| /// |
| /// Returns a new `LinkedHashMap<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 LinkedHashMap.fromEntries(Iterable<MapEntry<K, V>> entries) => |
| LinkedHashMap<K, V>()..addEntries(entries); |
| } |