Option<T> class sealed

An optional value.

An Option either contains a value (Some) or it does not (None).

Examples

The following function tries to multiply two integers after parsing them. Upon success, the resulting value is wrapped in a Some. If an error occurs during conversion, a None is returned.

Option<int> multiply(String a, String b) {
  return int
    .tryParse(a)
    .optional
    .zip(int.tryParse(b).optional)
    .map((ab) => ab.$1 * ab.$2);
}

That function can now be used to try and multiply two integers encoded as strings and returning None if that operation is not possible due to a conversion error.

// prints "Some(6)"
print(multiply('2', '3'));

// prints "None"
print(multiply('two', '3'));

Implementers

None
Some

Available Extensions

Annotations

@immutable

Constructors

Option(T? value): Creates a Some with the given value, if it is not null, or a None otherwise.
factory
Option.none(): Creates a None.
const

factory
Option.some(T value): Creates a Some with the given value.
const

factory

Properties

hashCode → int: The hash code for this object.
no setterinherited
isNone → bool: Whether this is a None.
no setter
isSome → bool: Whether this is a Some.
no setter
iterable → Iterable<T>: Returns an iterable over the possibly contained value.
no setter
runtimeType → Type: A representation of the runtime type of the object.
no setterinherited
valueOrNull → T?: The contained value if this is a Some, or null otherwise.
no setter

Methods

and(Option other) → Option: Returns other if this is a Some, or None otherwise.
andThen(Option calculateOther(T value)) → Option: Returns the result of calculateOther if this is a Some, or None otherwise.
contains(T value) → bool: Returns true if this is a Some of the given value.
inspect(void inspect(T value)) → Option<T>: Calls inspect with the contained value if this is a Some.
isSomeAnd(bool condition(T value)) → bool: Returns true if this is a Some with a contained value that satisfies condition.
map(U map(T value)) → Option: Transforms the contained value, if any, by applying map to it.
mapOr(U map(T value), U defaultValue) → U: Returns the contained value, if any, with map applied to it, or defaultValue otherwise.
mapOrElse(U map(T value), U calculateDefaultValue()) → U: Returns the contained value, if any, with map applied to it, or the result of calculateDefaultValue otherwise.
noSuchMethod(Invocation invocation) → dynamic: Invoked when a nonexistent method or property is accessed.
inherited
okOr<E>(E error) → Result<T, E>: Transforms an Option into a Result, mapping Some to an Ok of the contained value and None to Err of error.
okOrElse<E>(E calculateError()) → Result<T, E>: Transforms an Option into a Result, mapping Some to an Ok of the contained value and None to Err of the result of calculateError.
or(Option<T> other) → Option<T>: Returns a Some of the original value if this is a Some, or other otherwise.
orElse(Option<T> calculateOther()) → Option<T>: Returns a Some of the original value if this is a Some, or the result of calculateOther otherwise.
toString() → String: A string representation of this object.
inherited
unwrap({String? msg}) → T: Returns the contained value.
unwrapOr(T defaultValue) → T: Returns the contained value, if any, or defaultValue otherwise.
unwrapOrElse(T calculateDefaultValue()) → T: Returns the contained value, if any, or the result of calculateDefaultValue otherwise.
where(bool condition(T value)) → Option<T>: Returns a Some of the original value if this is a Some and its contained value satisfies condition, or None otherwise.
whereType() → Option: Returns a Some of the original value if this is a Some with a contained value of type U, or None otherwise.
xor(Option<T> other) → Option<T>: Returns a Some if either, but not both, of this and other is a Some, or None otherwise.
zip(Option other) → Option<(T, U)>: Returns a tuple of both this and other if both are Some, or None otherwise.
zipWith<U, R>(Option other, R zip(T value, U otherValue)) → Option<R>: Returns the result of zip called with both this and other if both are Some, or None otherwise.

Operators

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

Static Methods

collect<T>(Option<T> collector(U check(Option option))) → Option<T>: Encloses any number of operations, optionally returning early on None.
collectAsync<T>(FutureOr<Option<T>> collector(U check(Option option))) → Future<Option<T>>: Encloses any number of operations, optionally returning early on None.