description

# Set<E> class abstract interface

A collection of objects in which each object can occur only once.

That is, for each object of the element type, the object is either considered to be in the set, or to not be in the set.

Set implementations may consider some elements indistinguishable. These elements are treated as being the same for any operation on the set.

The default Set implementation, LinkedHashSet, considers objects indistinguishable if they are equal with regard to Object.== and Object.hashCode.

Iterating over elements of a set may be either unordered or ordered in some way. Examples:

- A HashSet is unordered, which means that its iteration order is unspecified,
- LinkedHashSet iterates in the insertion order of its elements, and
- a sorted set like SplayTreeSet iterates the elements in sorted order.

It is generally not allowed to modify the set (add or remove elements) while an operation on the set is being performed, for example during a call to forEach or containsAll. Nor is it allowed to modify the set while iterating either the set itself or any Iterable that is backed by the set, such as the ones returned by methods like where and map.

It is generally not allowed to modify the equality of elements (and thus not their hashcode) while they are in the set. Some specialized subtypes may be more permissive, in which case they should document this behavior.

Implemented types
  - Iterable<E>
Implementers
  - CssClassSet
  - HashSet
  - LinkedHashSet
  - SetBase
  - UnmodifiableSetView
Available extensions
  - EnumByName
  - FutureIterable
  - IterableExtensions
  - IterableToJSIterable
  - NullableIterableExtensions

## Constructors

Set()
  Creates an empty Set.
  factory
Set.from(Iterable elements)
  Creates a Set that contains all `elements`.
  factory
Set.identity()
  Creates an empty identity Set.
  factory
Set.of(Iterable<E> elements)
  Creates a Set from `elements`.
  factory
Set.unmodifiable(Iterable<E> elements)
  Creates an unmodifiable Set from `elements`.
  factory

## Properties

first → E
  The first element.
  no setterinherited
firstOrNull → T?

  Available on Iterable<T>, provided by the IterableExtensions extension

  The first element of this iterator, or `null` if the iterable is empty.
  no setter
hashCode → int
  The hash code for this object.
  no setterinherited
indexed → Iterable<(int, T)>

  Available on Iterable<T>, provided by the IterableExtensions extension

  Pairs of elements of the indices and elements of this iterable.
  no setter
isEmpty → bool
  Whether this collection has no elements.
  no setterinherited
isNotEmpty → bool
  Whether this collection has at least one element.
  no setterinherited
iterator → Iterator<E>
  An iterator that iterates over the elements of this set.
  no setteroverride
last → E
  The last element.
  no setterinherited
lastOrNull → T?

  Available on Iterable<T>, provided by the IterableExtensions extension

  The last element of this iterable, or `null` if the iterable is empty.
  no setter
length → int
  The number of elements in this Iterable.
  no setterinherited
nonNulls → Iterable<T>

  Available on Iterable<T?>, provided by the NullableIterableExtensions extension

  The non-`null` elements of this iterable.
  no setter
runtimeType → Type
  A representation of the runtime type of the object.
  no setterinherited
single → E
  Checks that this iterable has only one element, and returns that element.
  no setterinherited
singleOrNull → T?

  Available on Iterable<T>, provided by the IterableExtensions extension

  The single element of this iterator, or `null`.
  no setter
toJSIterable → JSIterable<T>

  Available on Iterable<T>, provided by the IterableToJSIterable extension

  A JSIterable wrapper that proxies to the Dart iterable API.
  no setter
wait → Future<List<T>>

  Available on Iterable<Future<T>>, provided by the FutureIterable extension

  Waits for futures in parallel.
  no setter

## Methods

add(E value) → bool
  Adds `value` to the set.
addAll(Iterable<E> elements) → void
  Adds all `elements` to this set.
any(bool test(E value)) → bool
  Checks whether any element of this iterable satisfies `test`.
  inherited
asNameMap() → Map<String, T>

  Available on Iterable<T>, provided by the EnumByName extension

  Creates a map from the names of enum values to the values.
byName(String name) → T

  Available on Iterable<T>, provided by the EnumByName extension

  Finds the enum value in this list with name `name`.
cast<R>() → Set<R>
  Provides a view of this set as a set of `R` instances.
  override
clear() → void
  Removes all elements from the set.
contains(Object? value) → bool
  Whether `value` is in the set.
  override
containsAll(Iterable<Object?> other) → bool
  Whether this set contains all the elements of `other`.
difference(Set<Object?> other) → Set<E>
  Creates a new set with the elements of this that are not in `other`.
elementAt(int index) → E
  Returns the `index`th element.
  inherited
elementAtOrNull(int index) → T?

  Available on Iterable<T>, provided by the IterableExtensions extension

  The element at position `index` of this iterable, or `null`.
every(bool test(E value)) → bool
  Checks whether every element of this iterable satisfies `test`.
  inherited
expand<T>(Iterable<T> toElements(E element)) → Iterable<T>
  Expands each element of this Iterable into zero or more elements.
  inherited
firstWhere(bool test(E value), {E orElse()?}) → E
  The first element that satisfies the given predicate `test`.
  inherited
fold<T>(T initialValue, T combine(T previousValue, E element)) → T
  Reduces a collection to a single value by iteratively combining each element of the collection with an existing value
  inherited
followedBy(Iterable<E> other) → Iterable<E>
  Creates the lazy concatenation of this iterable and `other`.
  inherited
forEach(void action(E element)) → void
  Invokes `action` on each element of this iterable in iteration order.
  inherited
intersection(Set<Object?> other) → Set<E>
  Creates a new set which is the intersection between this set and `other`.
join([String separator = ""]) → String
  Converts each element to a String and concatenates the strings.
  inherited
lastWhere(bool test(E value), {E orElse()?}) → E
  The last element that satisfies the given predicate `test`.
  inherited
lookup(Object? object) → E?
  If an object equal to `object` is in the set, return it.
map<T>(T toElement(E e)) → Iterable<T>
  The current elements of this iterable modified by `toElement`.
  inherited
noSuchMethod(Invocation invocation) → dynamic
  Invoked when a nonexistent method or property is accessed.
  inherited
reduce(E combine(E value, E element)) → E
  Reduces a collection to a single value by iteratively combining elements of the collection using the provided function.
  inherited
remove(Object? value) → bool
  Removes `value` from the set.
removeAll(Iterable<Object?> elements) → void
  Removes each element of `elements` from this set.
removeWhere(bool test(E value)) → void
  Removes all elements of this set that satisfy `test`.
retainAll(Iterable<Object?> elements) → void
  Removes all elements of this set that are not elements in `elements`.
retainWhere(bool test(E value)) → void
  Removes all elements of this set that fail to satisfy `test`.
singleWhere(bool test(E value), {E orElse()?}) → E
  The single element that satisfies `test`.
  inherited
skip(int count) → Iterable<E>
  Creates an Iterable that provides all but the first `count` elements.
  inherited
skipWhile(bool test(E value)) → Iterable<E>
  Creates an `Iterable` that skips leading elements while `test` is satisfied.
  inherited
take(int count) → Iterable<E>
  Creates a lazy iterable of the `count` first elements of this iterable.
  inherited
takeWhile(bool test(E value)) → Iterable<E>
  Creates a lazy iterable of the leading elements satisfying `test`.
  inherited
toList({bool growable = true}) → List<E>
  Creates a List containing the elements of this Iterable.
  inherited
toSet() → Set<E>
  Creates a Set with the same elements and behavior as this `Set`.
  override
toString() → String
  A string representation of this object.
  inherited
union(Set<E> other) → Set<E>
  Creates a new set which contains all the elements of this set and `other`.
where(bool test(E value)) → Iterable<E>
  Creates a new lazy Iterable with all elements that satisfy the predicate `test`.
  inherited
whereType<T>() → Iterable<T>
  Creates a new lazy Iterable with all elements that have type `T`.
  inherited

## Operators

operator ==(Object other) → bool
  The equality operator.
  inherited

## Static Methods

castFrom<S, T>(Set<S> source, {Set<R> newSet<R>()?}) → Set<T>
  Adapts `source` to be a `Set<T>`.
  override