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// 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 `==`.
*
* The map allows `null` as a key.
*/
abstract class LinkedHashMap<K, V> implements HashMap<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 [[]], [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 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.
*/
factory LinkedHashMap(
{bool equals(K key1, K key2),
int hashCode(K key),
bool isValidKey(potentialKey)}) {
if (isValidKey == null) {
if (hashCode == null) {
if (equals == null) {
return new _InternalLinkedHashMap<K, V>();
}
hashCode = _defaultHashCode;
} else {
if (identical(identityHashCode, hashCode) &&
identical(identical, equals)) {
return new _CompactLinkedIdentityHashMap<K, V>();
}
if (equals == null) {
equals = _defaultEquals;
}
}
} else {
if (hashCode == null) {
hashCode = _defaultHashCode;
}
if (equals == null) {
equals = _defaultEquals;
}
}
return new _CompactLinkedCustomHashMap<K, V>(equals, hashCode, isValidKey);
}
/**
* Creates an insertion-ordered identity-based map.
*
* Effectively a shorthand for:
*
* new LinkedHashMap<K, V>(equals: identical,
* hashCode: identityHashCode)
*/
factory LinkedHashMap.identity() = _CompactLinkedIdentityHashMap<K, V>;
/**
* Creates a [LinkedHashMap] that contains all key value pairs of [other].
*/
factory LinkedHashMap.from(Map other) {
LinkedHashMap<K, V> result = new LinkedHashMap<K, V>();
other.forEach((k, v) {
result[k as Object/*=K*/] = v as Object/*=V*/;
});
return result;
}
/**
* 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 key(element), V value(element)}) {
LinkedHashMap<K, V> map = new LinkedHashMap<K, V>();
Maps._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 = new LinkedHashMap<K, V>();
Maps._fillMapWithIterables(map, keys, values);
return map;
}
/// Holds a double-linked list of entries in insertion order.
/// The fields have the same name as the ones in [_LinkedHashMapEntry],
/// and this map is itself used as the head entry of the list.
/// Set to `this` when initialized, representing the empty list (containing
/// only the head entry itself).
var _nextEntry;
var _previousEntry;
}