| // 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 `==`. |
| /// |
| /// 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 Set<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 you supply one of [equals] and [hashCode], |
| /// you should generally also to supply the other. |
| /// |
| /// Some [equals] or [hashCode] functions might not work for all objects. |
| /// If [isValidKey] is supplied, it's used to check a potential element |
| /// which is not necessarily an instance of [E], like the argument to |
| /// [contains] which is typed as `Object?`. |
| /// If [isValidKey] returns `false`, for an object, the [equals] and |
| /// [hashCode] functions are not called, and no key equal to that object |
| /// is assumed to be in the map. |
| /// The [isValidKey] function defaults to just testing if the object is an |
| /// instance of [E], which means that: |
| /// ```dart template:expression |
| /// 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]. |
| external factory LinkedHashSet( |
| {bool Function(E, E)? equals, |
| int Function(E)? hashCode, |
| bool Function(dynamic)? isValidKey}); |
| |
| /// Creates an insertion-ordered identity-based set. |
| /// |
| /// Effectively a shorthand for: |
| /// ```dart |
| /// LinkedHashSet<E>(equals: identical, hashCode: identityHashCode) |
| /// ``` |
| external factory LinkedHashSet.identity(); |
| |
| /// 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 instances of [E]. |
| /// The `elements` iterable itself may have any element type, |
| /// so this constructor can be used to down-cast a `Set`, for example as: |
| /// ```dart |
| /// Set<SuperType> superSet = ...; |
| /// Iterable<SuperType> tmp = superSet.where((e) => e is SubType); |
| /// Set<SubType> subSet = LinkedHashSet<SubType>.from(tmp); |
| /// ``` |
| factory LinkedHashSet.from(Iterable<dynamic> elements) { |
| LinkedHashSet<E> result = LinkedHashSet<E>(); |
| for (final element in elements) { |
| result.add(element as E); |
| } |
| return result; |
| } |
| |
| /// Create a linked hash set from [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. |
| factory LinkedHashSet.of(Iterable<E> elements) => |
| LinkedHashSet<E>()..addAll(elements); |
| |
| /// 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; |
| } |