Introduction to HashSet in Dart:
The HashSet class of Dart is used for a hash-table based Set implementation. The Set collection is used to hold unique elements, i.e. we can’t have any duplicates in a set. The elements of a HashSet should provide an equivalence relation and should provide an implementation of hashCode.
It is unordered. So, the iteration order might differ. The HashSet class provides a couple of properties and methods.
Constructors of a HashSet:
There are four constructors available for a HashSet.
HashSet({bool equals(E, E)?, int hashCode(E)?, bool isValidKey(dynamic)?})
This constructor is used to create one HashSet and it uses the equals method as the equality method, hashCode method for the hash-code.
HashSet.from(Iterable it)
It creates one HashSet with all the items of the iterable it.
HashSet.identity()
It creates one identity-based HashSet.
HashSet.of(Iterable it)
Creates one HashSet with all the items of the iterable it.
Properties of a HashSet:
The following properties are available for a HashSet:
isEmpty → bool
Check if the HashSet is empty.
isNotEmpty → bool
Check if the HashSet is not empty.
length → int
Get the length of the HashSet.
first → E
Get the first element.
last → E
Get the last element.
single → E
Check if it has only one element and returns that.
iterator → Iterator
Get an iterator to iterate over the HashSet.
hashCode → int
Get the hashCode.
runtimeType → Type
Get the runtime type.
Methods of HashSet:
The following methods are available for a HashSet:
remove(Object? o) → bool
It removes the object o from the HashSet.
removeAll(Iterable<Object?> it) → void
Remove all the elements of the set.
clear() → void
It removes all elements of the HashSet
removeWhere(bool fn(E e)) → void
Removes all elements as defined by the function fn.
retainAll(Iterable<Object?> it) → void
Removes all elements that are not in the iterable it.
retainWhere(bool fn(E e)) → void
Removes all elements that are failed to the function fn.
add(E e) → bool
Add the element e to the HashSet.
addAll(Iterable it) → void
Adds all the elements of the iterable it to this set.
contains(Object? o) → bool
Check if the object o is in the HashSet or not.
containsAll(Iterable<Object?> it) → bool
This method can be used to check if all the items of the iterable are in the HashSet or not.
any(bool fn(E e)) → bool
Find if any element in the set satisfies the function fn.
every(bool fn(E e)) → bool
Find if all elements of the set satisfy the function fn.
elementAt(int i) → E
Return the element at index i of the HashSet.
firstWhere(bool fn(E element), {E orElse()?}) → E
Get the first element that satisfies the fn.
singleWhere(bool fn(E element), {E orElse()?}) → E
Get the single element that satisfies the fn.
lastWhere(bool fn(E element), {E orElse()?}) → E
Get the last element that satisfies the fn.
lookup(Object? o) → E?
Get the element equal to o in the set.
difference(Set<Object?> o) → Set
Get a new set with the elements that are in the current set but not in o.
intersection(Set<Object?> o) → Set
Get the intersection between the current set and o.
union(Set o) → Set
Get the union of the elements of the current set and the o.
skip(int count) → Iterable
Get one iterable by skipping the first count elements of the set.
skipWhile(bool fn(E e)) → Iterable
Get one iterable by skipping all the elements defined by the function fn.
forEach(void fn(E e)) → void
Call the function fn on each of the elements of the set.
map(T toElement(E e)) → Iterable
Modify the elements by the toElement function.
take(int count) → Iterable
Get one lazy iterable of the first count elements of the set.
takeWhile(bool fn(E e)) → Iterable
Get one lazy iterable of the first elements defined by the function fn.
where(bool fn(E e)) → Iterable
Get one lazy iterable of the elements satisfied by the predicate fn.
whereType() → Iterable
Get one lazy iterable of the elements of type T.
followedBy(Iterable it) → Iterable
Get one lazy iterable of this set and it.
reduce(E combine(E v, E e)) → E
Reduce the set to a single value by combining iteratively with the combine function.
fold(T initial, T combine(T previous, E element)) → T
It is similar to the reduce function, but it uses an initial value with the combine function.
expand(Iterable toElements(E e)) → Iterable
Expand each of the items of the set to one or more elements.
join([String separator = ""]) → String
Returns one string by concatenating the elements of the HashSet. It converts the elements to string.
toList({bool growable = true}) → List
It returns one list with the set elements.
toSet() → Set
Get one set with the elements of the HashSet.
toString() → String
Get the string representation of the HashSet.
cast() → Set
Get a set of R instance.
noSuchMethod(Invocation invocation) → dynamic
This is invoked if any undefined method is called.
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