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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 [LinkedHashSet] is a hash-table based [Set] implementation.
*
* The `LinkedHashSet` also keep track of the order that elements were inserted
* in, and iteration happens in first-to-last insertion order.
*
* The elements of a `LinkedHashSet` must have consistent [Object.==]
* and [Object.hashCode] implementations. This means that the `==` operator
* must define a stable equivalence relation on the elements (reflexive,
* symmetric, transitive, and consistent over time), and that `hashCode`
* must be the same for objects that are considered equal by `==`.
*
* The set allows `null` as an element.
*
* Iteration of elements is done in element insertion order.
* An element that was added after another will occur later in the iteration.
* Adding an element that is already in the set
* does not change its position in the iteration order,
* but removing an element and adding it again,
* will make it the last element of an iteration.
*
* Most simple operations on `HashSet` are done in (potentially amortized)
* constant time: [add], [contains], [remove], and [length], provided the hash
* codes of objects are well distributed..
*/
abstract class LinkedHashSet<E> implements HashSet<E> {
/**
* Create an insertion-ordered hash set using the provided
* [equals] and [hashCode].
*
* The provided [equals] must define a stable equivalence relation, and
* [hashCode] must be consistent with [equals]. If the [equals] or [hashCode]
* methods won't work on all objects, but only on some instances of E, the
* [isValidKey] predicate can be used to restrict the keys that the functions
* are applied to.
* Any key for which [isValidKey] returns false is automatically assumed
* to not be in the set when asking `contains`.
*
* If [equals] or [hashCode] are omitted, the set uses
* the elements' intrinsic [Object.==] and [Object.hashCode],
* and [isValidKey] is ignored since these operations are assumed
* to work on all objects.
*
* If you supply one of [equals] and [hashCode],
* you should generally also to supply the other.
*
* If the supplied `equals` or `hashCode` functions won't work on all [E]
* objects, and the map will be used in a setting where a non-`E` object
* is passed to, e.g., `contains`, then the [isValidKey] function should
* also be supplied.
*
* If [isValidKey] is omitted, it defaults to testing if the object is an
* [E] instance. That means that:
*
* new LinkedHashSet<int>(equals: (int e1, int e2) => (e1 - e2) % 5 == 0,
* hashCode: (int e) => e % 5)
*
* does not need an `isValidKey` argument, because it defaults to only
* accepting `int` values which are accepted by both `equals` and `hashCode`.
*
* If neither `equals`, `hashCode`, nor `isValidKey` is provided,
* the default `isValidKey` instead accepts all values.
* 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 set is identity based,
* and the `isValidKey` defaults to accepting all keys.
* Such a map can be created directly using [LinkedHashSet.identity].
*/
factory LinkedHashSet(
{bool equals(E e1, E e2),
int hashCode(E e),
bool isValidKey(potentialKey)}) {
if (isValidKey == null) {
if (hashCode == null) {
if (equals == null) {
return new _CompactLinkedHashSet<E>();
}
hashCode = _defaultHashCode;
} else {
if (identical(identityHashCode, hashCode) &&
identical(identical, equals)) {
return new _CompactLinkedIdentityHashSet<E>();
}
if (equals == null) {
equals = _defaultEquals;
}
}
} else {
if (hashCode == null) {
hashCode = _defaultHashCode;
}
if (equals == null) {
equals = _defaultEquals;
}
}
return new _CompactLinkedCustomHashSet<E>(equals, hashCode, isValidKey);
}
/**
* Creates an insertion-ordered identity-based set.
*
* Effectively a shorthand for:
*
* new LinkedHashSet<E>(equals: identical,
* hashCode: identityHashCode)
*/
factory LinkedHashSet.identity() = _CompactLinkedIdentityHashSet<E>;
/**
* Create a linked hash set containing all [elements].
*
* Creates a linked hash set as by `new LinkedHashSet<E>()` and adds each
* element of `elements` to this set in the order they are iterated.
*
* All the [elements] should be assignable to [E].
* The `elements` iterable itself may have any element type,
* so this constructor can be used to down-cast a `Set`, for example as:
*
* Set<SuperType> superSet = ...;
* Iterable<SuperType> tmp = superSet.where((e) => e is SubType);
* Set<SubType> subSet = new LinkedHashSet<SubType>.from(tmp);
*/
factory LinkedHashSet.from(Iterable elements) {
LinkedHashSet<E> result = new LinkedHashSet<E>();
for (final element in elements) {
E e = element as Object/*=E*/;
result.add(e);
}
return result;
}
/**
* Executes a function on each element of the set.
*
* The elements are iterated in insertion order.
*/
void forEach(void action(E element));
/**
* Provides an iterator that iterates over the elements in insertion order.
*/
Iterator<E> get iterator;
}