# HashSet<E> class

An unordered hash-table based Set implementation.

The elements of a `HashSet` must have consistent equality and hashCode implementations. This means that the equals operation must define a stable equivalence relation on the elements (reflexive, symmetric, transitive, and consistent over time), and that the hashCode must consistent with equality, so that the same for objects that are considered equal.

The set allows `null` as an element.

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.

The iteration order of the set is not specified and depends on the hashcodes of the provided elements. However, the order is stable: multiple iterations over the same set produce the same order, as long as the set is not modified.

Implements
  - Set<E>

## Constructors

HashSet({bool equals(E e1, E e2), int hashCode(E e), bool isValidKey(dynamic potentialKey) })
  Create a hash set using the provided `equals` as equality. [...]
  factory
HashSet.from(Iterable elements)
  Create a hash set containing all `elements`. [...]
  factory
HashSet.identity()
  Creates an unordered identity-based set. [...]
  factory
HashSet.of(Iterable<E> elements)
  Create a hash set containing all `elements`. [...]
  factory

## Properties

iterator → Iterator<E>
  Provides an iterator that iterates over the elements of this set. [...]
  read-only
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
last → E
  Returns the last element. [...]
  read-only, inherited
length → int
  Returns the number of elements in the iterable. [...]
  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. [...]
  inherited
addAll(Iterable<E> elements) → void
  Adds all `elements` to this Set. [...]
  inherited
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. [...]
  inherited
clear() → void
  Removes all elements in the set.
  inherited
contains(Object value) → bool
  Returns true if `value` is in the set.
  inherited
containsAll(Iterable<Object> other) → bool
  Returns whether this Set contains all the elements of `other`.
  inherited
difference(Set<Object> other) → Set<E>
  Returns a new set with the elements of this that are not in `other`. [...]
  inherited
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`. [...]
  inherited
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. [...]
  inherited
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.
  inherited
removeAll(Iterable<Object> elements) → void
  Removes each element of `elements` from this set.
  inherited
removeWhere(bool test(E element)) → void
  Removes all elements of this set that satisfy `test`.
  inherited
retainAll(Iterable<Object> elements) → void
  Removes all elements of this set that are not elements in `elements`. [...]
  inherited
retainWhere(bool test(E element)) → void
  Removes all elements of this set that fail to satisfy `test`.
  inherited
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. [...]
  inherited
toString() → String
  Returns a string representation of this object.
  inherited
union(Set<E> other) → Set<E>
  Returns a new set which contains all the elements of this set and `other`. [...]
  inherited
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 ==(dynamic other) → bool
  The equality operator. [...]
  inherited