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Change-Id: Id4a5e5b100ca1c429070263555ab730622644d19 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/127161 Reviewed-by: Leaf Petersen <leafp@google.com> Commit-Queue: Nicholas Shahan <nshahan@google.com>
142 lines
6 KiB
Dart
142 lines
6 KiB
Dart
// Copyright (c) 2013, the Dart project authors. Please see the AUTHORS file
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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part of dart.collection;
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/// A hash-table based implementation of [Map].
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///
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/// The insertion order of keys is remembered,
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/// and keys are iterated in the order they were inserted into the map.
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/// Values are iterated in their corresponding key's order.
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/// Changing a key's value, when the key is already in the map,
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/// does not change the iteration order,
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/// but removing the key and adding it again
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/// will make it be last in the iteration order.
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///
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/// The keys of a `LinkedHashMap` must have consistent [Object.==]
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/// and [Object.hashCode] implementations. This means that the `==` operator
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/// must define a stable equivalence relation on the keys (reflexive,
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/// symmetric, transitive, and consistent over time), and that `hashCode`
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/// must be the same for objects that are considered equal by `==`.
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///
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/// The map allows `null` as a key.
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abstract class LinkedHashMap<K, V> implements Map<K, V> {
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/// Creates an insertion-ordered hash-table based [Map].
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///
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/// If [equals] is provided, it is used to compare the keys in the table with
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/// new keys. If [equals] is omitted, the key's own [Object.==] is used
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/// instead.
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///
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/// Similar, if [hashCode] is provided, it is used to produce a hash value
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/// for keys in order to place them in the hash table. If it is omitted, the
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/// key's own [Object.hashCode] is used.
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///
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/// If using methods like [operator []], [remove] and [containsKey] together
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/// with a custom equality and hashcode, an extra `isValidKey` function
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/// can be supplied. This function is called before calling [equals] or
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/// [hashCode] with an argument that may not be a [K] instance, and if the
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/// call returns false, the key is assumed to not be in the set.
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/// The [isValidKey] function defaults to just testing if the object is a
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/// [K] instance.
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///
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/// Example:
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///
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/// new LinkedHashMap<int,int>(equals: (int a, int b) => (b - a) % 5 == 0,
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/// hashCode: (int e) => e % 5)
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///
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/// This example map does not need an `isValidKey` function to be passed.
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/// The default function accepts only `int` values, which can safely be
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/// passed to both the `equals` and `hashCode` functions.
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///
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/// If neither `equals`, `hashCode`, nor `isValidKey` is provided,
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/// the default `isValidKey` instead accepts all keys.
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/// The default equality and hashcode operations are assumed to work on all
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/// objects.
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///
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/// Likewise, if `equals` is [identical], `hashCode` is [identityHashCode]
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/// and `isValidKey` is omitted, the resulting map is identity based,
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/// and the `isValidKey` defaults to accepting all keys.
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/// Such a map can be created directly using [LinkedHashMap.identity].
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///
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/// The used `equals` and `hashCode` method should always be consistent,
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/// so that if `equals(a, b)` then `hashCode(a) == hashCode(b)`. The hash
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/// of an object, or what it compares equal to, should not change while the
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/// object is in the table. If it does change, the result is unpredictable.
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///
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/// If you supply one of [equals] and [hashCode],
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/// you should generally also to supply the other.
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external factory LinkedHashMap(
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{bool Function(K, K)? equals,
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int Function(K)? hashCode,
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bool Function(dynamic)? isValidKey});
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/// Creates an insertion-ordered identity-based map.
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///
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/// Effectively a shorthand for:
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///
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/// new LinkedHashMap<K, V>(equals: identical,
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/// hashCode: identityHashCode)
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external factory LinkedHashMap.identity();
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/// Creates a [LinkedHashMap] that contains all key value pairs of [other].
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///
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/// The keys must all be instances of [K] and the values to [V].
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/// The [other] map itself can have any type.
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factory LinkedHashMap.from(Map<dynamic, dynamic> other) {
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LinkedHashMap<K, V> result = LinkedHashMap<K, V>();
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other.forEach((dynamic k, dynamic v) {
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result[k as K] = v as V;
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});
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return result;
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}
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/// Creates a [LinkedHashMap] that contains all key value pairs of [other].
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factory LinkedHashMap.of(Map<K, V> other) =>
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LinkedHashMap<K, V>()..addAll(other);
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/// Creates a [LinkedHashMap] where the keys and values are computed from the
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/// [iterable].
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///
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/// For each element of the [iterable] this constructor computes a key/value
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/// pair, by applying [key] and [value] respectively.
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///
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/// The keys of the key/value pairs do not need to be unique. The last
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/// occurrence of a key will simply overwrite any previous value.
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///
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/// If no values are specified for [key] and [value] the default is the
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/// identity function.
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factory LinkedHashMap.fromIterable(Iterable iterable,
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{K Function(dynamic element)? key, V Function(dynamic element)? value}) {
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LinkedHashMap<K, V> map = LinkedHashMap<K, V>();
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MapBase._fillMapWithMappedIterable(map, iterable, key, value);
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return map;
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}
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/// Creates a [LinkedHashMap] associating the given [keys] to [values].
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///
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/// This constructor iterates over [keys] and [values] and maps each element of
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/// [keys] to the corresponding element of [values].
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///
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/// If [keys] contains the same object multiple times, the last occurrence
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/// overwrites the previous value.
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///
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/// It is an error if the two [Iterable]s don't have the same length.
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factory LinkedHashMap.fromIterables(Iterable<K> keys, Iterable<V> values) {
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LinkedHashMap<K, V> map = LinkedHashMap<K, V>();
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MapBase._fillMapWithIterables(map, keys, values);
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return map;
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}
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/// Creates a [LinkedHashMap] containing the entries of [entries].
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///
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/// Returns a new `LinkedHashMap<K, V>` where all entries of [entries]
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/// have been added in iteration order.
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///
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/// If multiple [entries] have the same key,
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/// later occurrences overwrite the earlier ones.
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@Since("2.1")
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factory LinkedHashMap.fromEntries(Iterable<MapEntry<K, V>> entries) =>
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LinkedHashMap<K, V>()..addEntries(entries);
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}
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