Optional<T> class sealed

A container object which may or may not contain a value of type T.

Note that depending on the nullability of type T, a null value can be a perfectly valid present value.

Also see https://en.wikipedia.org/wiki/Option_type.

Annotations
  • @immutable

Constructors

Optional.absent()
Returns an absent Optional instance.
const
factory
Optional.of(T value)
Returns a present Optional of the given value.
const
factory
Optional.ofNullable(T? value)
Returns a present Optional of the given value if the value is non-null, otherwise an absent Optional instance.
factory

Properties

hashCode → int
The hash code for this object.
no setterinherited
isAbsent → bool
Returns whether the value is absent.
no setter
isPresent → bool
Returns whether the value is present.
no setter
iterable → Iterable<T>
Returns an Iterable with the single present value, otherwise an empty iterable.
no setter
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited
value → T
Returns the present value, otherwise throws a StateError.
no setter

Methods

flatMap<R>(Map1<T, Optional<R>> function) → Optional<R>
Transforms the present value of this Optional with the provided mapping function, otherwise returns an absent Optional.
ifAbsent(Callback0 function) → void
Evaluates the callback function if the value is absent, otherwise does nothing.
ifPresent(Callback1<T> function) → void
Evaluates the callback function with the present value, otherwise does nothing.
map<R>(Map1<T, R> function) → Optional<R>
Transforms the present value of this Optional with the provided mapping function, otherwise returns an absent Optional.
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent method or property is accessed.
inherited
or(Map0<Optional<T>> function) → Optional<T>
Returns the current optional if present, otherwise evaluates the function callback and returns its optional.
orElse(T value) → T
Returns the current value if present, otherwise the argument value.
orElseGet(Map0<T> function) → T
Returns the current value if present, otherwise evaluates the callback function and returns its value.
orElseThrow([Object? error]) → T
Returns the current value if present, otherwise throws the provided error or a StateError.
toString() → String
A string representation of this object.
inherited
where(Predicate1<T> function) → Optional<T>
Returns this Optional if the provided predicate function evaluates to true, otherwise returns an absent Optional.
whereType<R>() → Optional<R>
Casts the present value of this Optional to R, otherwise returns an absent Optional.

Operators

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