Ribs

Appearance

ribs_core›Classes›Option<A>

Option<A> sealed ​

sealedclassOption<A>

Annotations: @immutable

Represents optional values.

Instances of Option are either a Some or None. At first glance, Option may seem just like a nullable type (e.g. Option<int> <-> int?), but Option provides far more combinators to give greater power and flexibility. There are also conversions to move between optional and nullable types.

Implementers

Available Extensions

Constructors ​

Option() factory ​

factoryOption(A?a)

Creates an Option from the nullable value. If the value is null, a None will be returned. If the value is non-null, a Some will be returned.

Implementation
dart
factory Option(A? a) => a == null ? none<A>() : Some(a);

Option.pure() factory ​

factoryOption.pure(Aa)

Creates an Option (i.e. Some) from the given non-null value.

Implementation
dart
factory Option.pure(A a) => Some(a);

Option.unless() factory ​

factoryOption.unless(boolFunction()condition,AFunction()a)

Evaluates the given condition and returns None when the condition is true, or a Some with a value of the result of given function.

Implementation
dart
factory Option.unless(Function0<bool> condition, Function0<A> a) =>
    condition() ? const None() : Some(a());

Option.when() factory ​

factoryOption.when(boolFunction()condition,AFunction()a)

Evaluates the given condition and returns None when the condition is false, or a Some with a value of the result of given function.

Implementation
dart
factory Option.when(Function0<bool> condition, Function0<A> a) =>
    condition() ? Some(a()) : const None();

Properties ​

hashCode no setter override ​

intgethashCode

The hash code for this object.

A hash code is a single integer which represents the state of the object that affects operator == comparisons.

All objects have hash codes. The default hash code implemented by Object represents only the identity of the object, the same way as the default operator == implementation only considers objects equal if they are identical (see identityHashCode).

If operator == is overridden to use the object state instead, the hash code must also be changed to represent that state, otherwise the object cannot be used in hash based data structures like the default Set and Map implementations.

Hash codes must be the same for objects that are equal to each other according to operator ==. The hash code of an object should only change if the object changes in a way that affects equality. There are no further requirements for the hash codes. They need not be consistent between executions of the same program and there are no distribution guarantees.

Objects that are not equal are allowed to have the same hash code. It is even technically allowed that all instances have the same hash code, but if clashes happen too often, it may reduce the efficiency of hash-based data structures like HashSet or HashMap.

If a subclass overrides hashCode, it should override the operator == operator as well to maintain consistency.

Implementation
dart
@override
int get hashCode;

isDefined no setter ​

boolgetisDefined

Returns true if this Option is a Some, false if it's a None.

Implementation
dart
bool get isDefined => this is Some;

isEmpty no setter ​

boolgetisEmpty

Returns true if this is a None, false if it's a Some.

Implementation
dart
bool get isEmpty => this is None;

nonEmpty no setter ​

boolgetnonEmpty

Returns true if this is a Some, false if it's a None.

Implementation
dart
bool get nonEmpty => this is Some;

runtimeType no setter inherited ​

TypegetruntimeType

A representation of the runtime type of the object.

Inherited from Object.

Implementation
dart
external Type get runtimeType;

Extension Properties ​

get extension no setter ​

Agetget

Returns the value if this is a Some, or throws a StateError if this is a None.

This is an unsafe, partial operation. Prefer getOrElse, fold, or pattern matching when the Option may be None. Use get only when you have already proven that this Option is non-empty.

See also getOrNull for a nullable alternative, and getOrElse for providing a fallback value.

Available on Option<A>, provided by the OptionOps<A> extension

Implementation
dart
A get get => fold(() => throw StateError('None.get'), identity);

getOrNull extension no setter ​

A?getgetOrNull

Returns the value if this is a Some, or null if this is a None.

This is equivalent to Option.toNullable and is provided as a conventionally named companion to get.

Available on Option<A>, provided by the OptionOps<A> extension

Implementation
dart
A? get getOrNull => toNullable();

Methods ​

exists() ​

boolexists(boolFunction(A)p)

Returns true if this is a Some and the value satisfies p.

Implementation
dart
bool exists(Function1<A, bool> p) => fold(() => false, p);

filter() ​

Option<A>filter(boolFunction(A)p)

Returns this option if it is non-empty and p returns true for the value. Otherwise returns None.

Implementation
dart
Option<A> filter(Function1<A, bool> p);

filterNot() ​

Option<A>filterNot(boolFunction(A)p)

Returns this option if it is empty or p returns false for the value. Otherwise returns None.

Implementation
dart
Option<A> filterNot(Function1<A, bool> p) => filter((a) => !p(a));

flatMap() ​

Option<B>flatMap<B>(Option<B>Function(A)f)

Returns the result of applying f to the contained value if this is a Some, or None if this is a None.

Implementation
dart
Option<B> flatMap<B>(Function1<A, Option<B>> f);

fold() ​

Bfold<B>(BFunction()ifEmpty,BFunction(A)f)

Returns the result of applying f to this Option value if non-empty. Otherwise, returns the result of ifEmpty.

Implementation
dart
B fold<B>(Function0<B> ifEmpty, Function1<A, B> f);

foldLeft() ​

BfoldLeft<B>(Bz,BFunction(B,A)op)

Applies op to the seed z and the contained value, or returns z for None.

Implementation
dart
B foldLeft<B>(B z, Function2<B, A, B> op) => fold(() => z, (a) => op(z, a));

foldRight() ​

BfoldRight<B>(Bz,BFunction(A,B)op)

Applies op to the contained value and seed z, or returns z for None.

Implementation
dart
B foldRight<B>(B z, Function2<A, B, B> op) => fold(() => z, (a) => op(a, z));

forall() ​

boolforall(boolFunction(A)p)

Returns true if this is a None, or if the value satisfies p.

Implementation
dart
bool forall(Function1<A, bool> p) => fold(() => true, p);

foreach() ​

voidforeach<U>(UFunction(A)f)

Applies f to the value if this is a Some; does nothing for None.

Implementation
dart
void foreach<U>(Function1<A, U> f) => fold(() {}, f);

map() ​

Option<B>map<B>(BFunction(A)f)

Applies f to the contained value and wraps the result in Some, or returns None if this is a None.

Implementation
dart
Option<B> map<B>(Function1<A, B> f);

noSuchMethod() inherited ​

dynamicnoSuchMethod(Invocationinvocation)

Invoked when a nonexistent method or property is accessed.

A dynamic member invocation can attempt to call a member which doesn't exist on the receiving object. Example:

dart
dynamic object = 1;
object.add(42); // Statically allowed, run-time error

This invalid code will invoke the noSuchMethod method of the integer 1 with an Invocation representing the .add(42) call and arguments (which then throws).

Classes can override noSuchMethod to provide custom behavior for such invalid dynamic invocations.

A class with a non-default noSuchMethod invocation can also omit implementations for members of its interface. Example:

dart
class MockList<T> implements List<T> {
  noSuchMethod(Invocation invocation) {
    log(invocation);
    super.noSuchMethod(invocation); // Will throw.
  }
}
void main() {
  MockList().add(42);
}

This code has no compile-time warnings or errors even though the MockList class has no concrete implementation of any of the List interface methods. Calls to List methods are forwarded to noSuchMethod, so this code will log an invocation similar to Invocation.method(#add, [42]) and then throw.

If a value is returned from noSuchMethod, it becomes the result of the original invocation. If the value is not of a type that can be returned by the original invocation, a type error occurs at the invocation.

The default behavior is to throw a NoSuchMethodError.

Inherited from Object.

Implementation
dart
@pragma("vm:entry-point")
@pragma("wasm:entry-point")
external dynamic noSuchMethod(Invocation invocation);

toLeft() ​

Either<A,X>toLeft<X>(XFunction()ifEmpty)

If this is a Some a Left is returned with the value. If this is a None, a Right is returned with the result of evaluating ifEmpty.

Implementation
dart
Either<A, X> toLeft<X>(Function0<X> ifEmpty);

toNullable() ​

A?toNullable()

Returns a nullable value, which is the value itself if this is a Some, or null if this is a None.

Implementation
dart
A? toNullable();

toRight() ​

Either<X,A>toRight<X>(XFunction()ifEmpty)

If this is a Some a Right is returned with the value. If this is a None, a Left is returned with the result of evaluating ifEmpty.

Implementation
dart
Either<X, A> toRight<X>(Function0<X> ifEmpty);

toString() override ​

StringtoString()

A string representation of this object.

Some classes have a default textual representation, often paired with a static parse function (like int.parse). These classes will provide the textual representation as their string representation.

Other classes have no meaningful textual representation that a program will care about. Such classes will typically override toString to provide useful information when inspecting the object, mainly for debugging or logging.

Implementation
dart
@override
String toString() => fold(() => 'None', (a) => 'Some($a)');

Extension Methods ​

contains() extension ​

boolcontains(Aelem)

Returns true if this is a Some whose value equals elem.

Available on Option<A>, provided by the OptionOps<A> extension

Implementation
dart
bool contains(A elem) => fold(() => false, (value) => value == elem);

filterN() extension ​

Option<Record>filterN(boolFunction(T1,T2,T3)p)

Available on Option<A>, provided by the OptionTuple3Ops<T1, T2, T3> extension

Implementation
dart
Option<(T1, T2, T3)> filterN(Function3<T1, T2, T3, bool> p) => filter(p.tupled);

filterN() extension ​

Option<Record>filterN(boolFunction(T1,T2)p)

Available on Option<A>, provided by the OptionTuple2Ops<T1, T2> extension

Implementation
dart
Option<(T1, T2)> filterN(Function2<T1, T2, bool> p) => filter(p.tupled);

filterN() extension ​

Option<Record>filterN(boolFunction(T1,T2,T3,T4,T5)p)

Available on Option<A>, provided by the OptionTuple5Ops<T1, T2, T3, T4, T5> extension

Implementation
dart
Option<(T1, T2, T3, T4, T5)> filterN(Function5<T1, T2, T3, T4, T5, bool> p) => filter(p.tupled);

filterN() extension ​

Option<Record>filterN(boolFunction(T1,T2,T3,T4)p)

Available on Option<A>, provided by the OptionTuple4Ops<T1, T2, T3, T4> extension

Implementation
dart
Option<(T1, T2, T3, T4)> filterN(Function4<T1, T2, T3, T4, bool> p) => filter(p.tupled);

filterNotN() extension ​

Option<Record>filterNotN(boolFunction(T1,T2,T3)p)

Available on Option<A>, provided by the OptionTuple3Ops<T1, T2, T3> extension

Implementation
dart
Option<(T1, T2, T3)> filterNotN(Function3<T1, T2, T3, bool> p) => filterNot(p.tupled);

filterNotN() extension ​

Option<Record>filterNotN(boolFunction(T1,T2,T3,T4,T5)p)

Available on Option<A>, provided by the OptionTuple5Ops<T1, T2, T3, T4, T5> extension

Implementation
dart
Option<(T1, T2, T3, T4, T5)> filterNotN(Function5<T1, T2, T3, T4, T5, bool> p) =>
    filterNot(p.tupled);

filterNotN() extension ​

Option<Record>filterNotN(boolFunction(T1,T2,T3,T4)p)

Available on Option<A>, provided by the OptionTuple4Ops<T1, T2, T3, T4> extension

Implementation
dart
Option<(T1, T2, T3, T4)> filterNotN(Function4<T1, T2, T3, T4, bool> p) => filterNot(p.tupled);

filterNotN() extension ​

Option<Record>filterNotN(boolFunction(T1,T2)p)

Available on Option<A>, provided by the OptionTuple2Ops<T1, T2> extension

Implementation
dart
Option<(T1, T2)> filterNotN(Function2<T1, T2, bool> p) => filterNot(p.tupled);

flatMapN() extension ​

Option<T6>flatMapN<T6>(Option<T6>Function(T1,T2,T3,T4,T5)f,);

Available on Option<A>, provided by the OptionTuple5Ops<T1, T2, T3, T4, T5> extension

Implementation
dart
Option<T6> flatMapN<T6>(Function5<T1, T2, T3, T4, T5, Option<T6>> f) => flatMap(f.tupled);

flatMapN() extension ​

Option<T5>flatMapN<T5>(Option<T5>Function(T1,T2,T3,T4)f)

Available on Option<A>, provided by the OptionTuple4Ops<T1, T2, T3, T4> extension

Implementation
dart
Option<T5> flatMapN<T5>(Function4<T1, T2, T3, T4, Option<T5>> f) => flatMap(f.tupled);

flatMapN() extension ​

Option<T3>flatMapN<T3>(Option<T3>Function(T1,T2)f)

Available on Option<A>, provided by the OptionTuple2Ops<T1, T2> extension

Implementation
dart
Option<T3> flatMapN<T3>(Function2<T1, T2, Option<T3>> f) => flatMap(f.tupled);

flatMapN() extension ​

Option<T4>flatMapN<T4>(Option<T4>Function(T1,T2,T3)f)

Available on Option<A>, provided by the OptionTuple3Ops<T1, T2, T3> extension

Implementation
dart
Option<T4> flatMapN<T4>(Function3<T1, T2, T3, Option<T4>> f) => flatMap(f.tupled);

flatten() extension ​

Option<A>flatten()

If this is a Some, the value is returned, otherwise None is returned.

Available on Option<A>, provided by the OptionNestedOps<A> extension

Implementation
dart
Option<A> flatten() => fold(() => none<A>(), identity);

foldN() extension ​

T6foldN<T6>(T6Function()ifEmpty,T6Function(T1,T2,T3,T4,T5)ifSome,);

Available on Option<A>, provided by the OptionTuple5Ops<T1, T2, T3, T4, T5> extension

Implementation
dart
T6 foldN<T6>(
  Function0<T6> ifEmpty,
  Function5<T1, T2, T3, T4, T5, T6> ifSome,
) => fold(ifEmpty, ifSome.tupled);

foldN() extension ​

T5foldN<T5>(T5Function()ifEmpty,T5Function(T1,T2,T3,T4)ifSome,);

Available on Option<A>, provided by the OptionTuple4Ops<T1, T2, T3, T4> extension

Implementation
dart
T5 foldN<T5>(
  Function0<T5> ifEmpty,
  Function4<T1, T2, T3, T4, T5> ifSome,
) => fold(ifEmpty, ifSome.tupled);

foldN() extension ​

T3foldN<T3>(T3Function()ifEmpty,T3Function(T1,T2)ifSome)

Available on Option<A>, provided by the OptionTuple2Ops<T1, T2> extension

Implementation
dart
T3 foldN<T3>(
  Function0<T3> ifEmpty,
  Function2<T1, T2, T3> ifSome,
) => fold(ifEmpty, ifSome.tupled);

foldN() extension ​

T4foldN<T4>(T4Function()ifEmpty,T4Function(T1,T2,T3)ifSome,);

Available on Option<A>, provided by the OptionTuple3Ops<T1, T2, T3> extension

Implementation
dart
T4 foldN<T4>(
  Function0<T4> ifEmpty,
  Function3<T1, T2, T3, T4> ifSome,
) => fold(ifEmpty, ifSome.tupled);

foreachN() extension ​

voidforeachN(voidFunction(T1,T2,T3,T4,T5)ifSome)

Available on Option<A>, provided by the OptionTuple5Ops<T1, T2, T3, T4, T5> extension

Implementation
dart
void foreachN(Function5<T1, T2, T3, T4, T5, void> ifSome) => foreach(ifSome.tupled);

foreachN() extension ​

voidforeachN(voidFunction(T1,T2,T3)ifSome)

Available on Option<A>, provided by the OptionTuple3Ops<T1, T2, T3> extension

Implementation
dart
void foreachN(Function3<T1, T2, T3, void> ifSome) => foreach(ifSome.tupled);

foreachN() extension ​

voidforeachN(voidFunction(T1,T2)ifSome)

Available on Option<A>, provided by the OptionTuple2Ops<T1, T2> extension

Implementation
dart
void foreachN(Function2<T1, T2, void> ifSome) => foreach(ifSome.tupled);

foreachN() extension ​

voidforeachN(voidFunction(T1,T2,T3,T4)ifSome)

Available on Option<A>, provided by the OptionTuple4Ops<T1, T2, T3, T4> extension

Implementation
dart
void foreachN(Function4<T1, T2, T3, T4, void> ifSome) => foreach(ifSome.tupled);

getOrElse() extension ​

AgetOrElse(AFunction()ifEmpty)

Returns the value if this is a Some or the value returned from evaluating ifEmpty.

Available on Option<A>, provided by the OptionOps<A> extension

Implementation
dart
A getOrElse(Function0<A> ifEmpty) => fold(ifEmpty, identity);

mapN() extension ​

Option<T3>mapN<T3>(T3Function(T1,T2)f)

Available on Option<A>, provided by the OptionTuple2Ops<T1, T2> extension

Implementation
dart
Option<T3> mapN<T3>(Function2<T1, T2, T3> f) => map(f.tupled);

mapN() extension ​

Option<T4>mapN<T4>(T4Function(T1,T2,T3)f)

Available on Option<A>, provided by the OptionTuple3Ops<T1, T2, T3> extension

Implementation
dart
Option<T4> mapN<T4>(Function3<T1, T2, T3, T4> f) => map(f.tupled);

mapN() extension ​

Option<T5>mapN<T5>(T5Function(T1,T2,T3,T4)f)

Available on Option<A>, provided by the OptionTuple4Ops<T1, T2, T3, T4> extension

Implementation
dart
Option<T5> mapN<T5>(Function4<T1, T2, T3, T4, T5> f) => map(f.tupled);

mapN() extension ​

Option<T6>mapN<T6>(T6Function(T1,T2,T3,T4,T5)f)

Available on Option<A>, provided by the OptionTuple5Ops<T1, T2, T3, T4, T5> extension

Implementation
dart
Option<T6> mapN<T6>(Function5<T1, T2, T3, T4, T5, T6> f) => map(f.tupled);

orElse() extension ​

Option<A>orElse(Option<A>Function()orElse)

If this is a Some, this is returned, otherwise the result of evaluating orElse is returned.

Available on Option<A>, provided by the OptionOps<A> extension

Implementation
dart
Option<A> orElse(Function0<Option<A>> orElse) => fold(orElse, (_) => this);

sequence() extension ​

IO<Option<A>>sequence()

Returns an IO that will return None if this is a None, or the evaluation of the IO lifted into an Option, specifically a Some.

Available on Option<A>, provided by the OptionIOOps<A> extension

Implementation
dart
IO<Option<A>> sequence() => fold(() => IO.pure(none()), (io) => io.map((a) => Some(a)));

traverseIO() extension ​

IO<Option<B>>traverseIO<B>(IO<B>Function(A)f)

If this is a Some, returns the result of applying f to the value, otherwise an IO with a None is returned.

Available on Option<A>, provided by the IOOptionOps<A> extension

Implementation
dart
IO<Option<B>> traverseIO<B>(Function1<A, IO<B>> f) =>
    fold(() => IO.none(), (a) => f(a).map((a) => Some(a)));

traverseIO_() extension ​

IO<Unit>traverseIO_<B>(IO<B>Function(A)f)

Same behavior as traverseIO but the resulting value is discarded.

Available on Option<A>, provided by the IOOptionOps<A> extension

Implementation
dart
IO<Unit> traverseIO_<B>(Function1<A, IO<B>> f) =>
    fold(() => IO.unit, (a) => f(a).map((_) => Unit()));

Operators ​

operator ==() override ​

booloperator ==(Objectother)

The equality operator.

The default behavior for all Objects is to return true if and only if this object and other are the same object.

Override this method to specify a different equality relation on a class. The overriding method must still be an equivalence relation. That is, it must be:

  • Total: It must return a boolean for all arguments. It should never throw.

  • Reflexive: For all objects o, o == o must be true.

  • Symmetric: For all objects o1 and o2, o1 == o2 and o2 == o1 must either both be true, or both be false.

  • Transitive: For all objects o1, o2, and o3, if o1 == o2 and o2 == o3 are true, then o1 == o3 must be true.

The method should also be consistent over time, so whether two objects are equal should only change if at least one of the objects was modified.

If a subclass overrides the equality operator, it should override the hashCode method as well to maintain consistency.

Implementation
dart
@override
bool operator ==(Object other);