Optional<T> class

A value that might be absent.

Use Optional as an alternative to allowing fields, parameters or return values to be null. It signals that a value is not required and provides convenience methods for dealing with the absent case.

Inheritance

Constructors

Optional.absent()
Constructs an empty Optional.
const
Optional.fromNullable(T value)
Constructs an Optional of the given value. [...]
const
Optional.of(T value)
Constructs an Optional of the given value. [...]

Properties

hashCode int
Delegates to the underlying value hashCode.
read-only, override
isNotPresent bool
True when this optional contains no value.
read-only
isPresent bool
True when this optional contains a value.
read-only
iterator Iterator<T>
Returns a new Iterator that allows iterating the elements of this Iterable. [...]
read-only, override
orNull → T
Gets the Optional value, or null if there is none.
read-only
value → T
Gets the Optional value. [...]
read-only
first → T
Returns the first element. [...]
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 → T
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 → T
Checks that this iterable has only one element, and returns that element. [...]
read-only, inherited

Methods

ifAbsent(void ifAbsent()) → void
Execution a function if the Optional value is absent.
ifPresent(void ifPresent(T value)) → void
Executes a function if the Optional value is present.
or(T defaultValue) → T
Gets the Optional value with a default. [...]
toString() String
Returns a string representation of (some of) the elements of this. [...]
override
transform<S>(S transformer(T value)) Optional<S>
Transforms the Optional value. [...]
transformNullable<S>(S transformer(T value)) Optional<S>
Transforms the Optional value. [...]
any(bool test(E element)) bool
Checks whether any element of this iterable satisfies test. [...]
inherited
cast<R>() Iterable<R>
Provides a view of this iterable as an iterable of R instances. [...]
inherited
contains(Object element) bool
Returns true if the collection contains an element equal to element. [...]
inherited
elementAt(int index) → T
Returns the indexth 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), { T orElse() }) → T
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<T> other) Iterable<T>
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
join([String separator = "" ]) String
Converts each element to a String and concatenates the strings. [...]
inherited
lastWhere(bool test(E element), { T orElse() }) → T
Returns the last element that satisfies the given predicate test. [...]
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(T combine(E value, E element)) → T
Reduces a collection to a single value by iteratively combining elements of the collection using the provided function. [...]
inherited
singleWhere(bool test(E element), { T orElse() }) → T
Returns the single element that satisfies test. [...]
inherited
skip(int count) Iterable<T>
Returns an Iterable that provides all but the first count elements. [...]
inherited
skipWhile(bool test(E value)) Iterable<T>
Returns an Iterable that skips leading elements while test is satisfied. [...]
inherited
take(int count) Iterable<T>
Returns a lazy iterable of the count first elements of this iterable. [...]
inherited
takeWhile(bool test(E value)) Iterable<T>
Returns a lazy iterable of the leading elements satisfying test. [...]
inherited
toList({bool growable: true }) List<T>
Creates a List containing the elements of this Iterable. [...]
inherited
toSet() Set<T>
Creates a Set containing the same elements as this iterable. [...]
inherited
where(bool test(E element)) Iterable<T>
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 o) bool
Delegates to the underlying value operator==.
override