description

# Set<E> class Null safety

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 operator Object.==.

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.

Inheritance
  - Object
  - Iterable<E>
  - Set
Implementers
  - CssClassSet
  - HashSet
  - LinkedHashSet
  - SetMixin

## 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

## Properties

first → E
  Returns the first element. [...]
  read-only, inherited
hashCode → int
  The hash code for this object. [...]
  read-only, inherited
isEmpty → bool
  Returns `true` if there are no elements in this collection. [...]
  read-only, inherited
isNotEmpty → bool
  Returns true if there is at least one element in this collection. [...]
  read-only, inherited
iterator → Iterator<E>
  Provides an iterator that iterates over the elements of this set. [...]
  read-only, override
last → E
  Returns the last element. [...]
  read-only, inherited
length → int
  Returns the number of elements in this. [...]
  read-only, inherited
runtimeType → Type
  A representation of the runtime type of the object.
  read-only, inherited
single → E
  Checks that this iterable has only one element, and returns that element. [...]
  read-only, inherited

## 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 element)) → bool
  Checks whether any element of this iterable satisfies `test`. [...]
  inherited
cast<R>() → Set<R>
  Provides a view of this set as a set of `R` instances. [...]
  override
clear() → void
  Removes all elements in the set.
contains(Object? value) → bool
  Returns true if `value` is in the set.
  override
containsAll(Iterable<Object?> other) → bool
  Returns whether this Set contains all the elements of `other`.
difference(Set<Object?> other) → Set<E>
  Returns a new set with the elements of this that are not in `other`. [...]
elementAt(int index) → E
  Returns the `index`th element. [...]
  inherited
every(bool test(E element)) → bool
  Checks whether every element of this iterable satisfies `test`. [...]
  inherited
expand<T>(Iterable<T> f(E element)) → Iterable<T>
  Expands each element of this Iterable into zero or more elements. [...]
  inherited
firstWhere(bool test(E element), {E orElse()}) → E
  Returns 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>
  Returns the lazy concatentation of this iterable and `other`. [...]
  inherited
forEach(void f(E element)) → void
  Applies the function `f` to each element of this collection in iteration order.
  inherited
intersection(Set<Object?> other) → Set<E>
  Returns 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 element), {E orElse()}) → E
  Returns 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 f(E e)) → Iterable<T>
  Returns a new lazy Iterable with elements that are created by calling `f` on each element of this `Iterable` in iteration order. [...]
  inherited
noSuchMethod(Invocation invocation) → dynamic
  Invoked when a non-existent 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. Returns true if `value` was in the set. Returns false otherwise. The method has no effect if `value` value was not in the set.
removeAll(Iterable<Object?> elements) → void
  Removes each element of `elements` from this set.
removeWhere(bool test(E element)) → 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 element)) → void
  Removes all elements of this set that fail to satisfy `test`.
singleWhere(bool test(E element), {E orElse()}) → E
  Returns the single element that satisfies `test`. [...]
  inherited
skip(int count) → Iterable<E>
  Returns an Iterable that provides all but the first `count` elements. [...]
  inherited
skipWhile(bool test(E value)) → Iterable<E>
  Returns an `Iterable` that skips leading elements while `test` is satisfied. [...]
  inherited
take(int count) → Iterable<E>
  Returns a lazy iterable of the `count` first elements of this iterable. [...]
  inherited
takeWhile(bool test(E value)) → Iterable<E>
  Returns 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 containing the same elements as this iterable. [...]
  override
toString() → String
  Returns a string representation of (some of) the elements of `this`. [...]
  inherited
union(Set<E> other) → Set<E>
  Returns a new set which contains all the elements of this set and `other`. [...]
where(bool test(E element)) → Iterable<E>
  Returns a new lazy Iterable with all elements that satisfy the predicate `test`. [...]
  inherited
whereType<T>() → Iterable<T>
  Returns 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()}) → Set<T>
  Adapts `source` to be a `Set<T>`. [...]
  override