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/Scala 2.13 Library

Object scala.None

object None extends Option[Nothing] with Product with Serializable

This case object represents non-existent values.

Annotations
@SerialVersionUID()
Source
Option.scala
Since

1.0

Linear Supertypes
Option[Nothing], java.io.Serializable, Product, Equals, collection.IterableOnce[Nothing], AnyRef, Any

Type Members

class WithFilter extends AnyRef

We need a whole WithFilter class to honor the "doesn't create a new collection" contract even though it seems unlikely to matter much in a collection with max size 1.

Definition Classes
Option

Value Members

final def !=(arg0: Any): Boolean

Test two objects for inequality.

returns

true if !(this == that), false otherwise.

Definition Classes
AnyRef → Any

final def ##(): Int

Equivalent to x.hashCode except for boxed numeric types and null. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. For null returns a hashcode where null.hashCode throws a NullPointerException.

returns

a hash value consistent with ==

Definition Classes
AnyRef → Any

final def ==(arg0: Any): Boolean

The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).

returns

true if the receiver object is equivalent to the argument; false otherwise.

Definition Classes
AnyRef → Any

final def asInstanceOf[T0]: T0

Cast the receiver object to be of type T0.

Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression 1.asInstanceOf[String] will throw a ClassCastException at runtime, while the expression List(1).asInstanceOf[List[String]] will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.

returns

the receiver object.

Definition Classes
Any
Exceptions thrown

ClassCastException if the receiver object is not an instance of the erasure of type T0.

def clone(): AnyRef

Create a copy of the receiver object.

The default implementation of the clone method is platform dependent.

returns

a copy of the receiver object.

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.CloneNotSupportedException]) @native()
Note

not specified by SLS as a member of AnyRef

final def collect[B](pf: PartialFunction[Nothing, B]): Option[B]

Returns a scala.Some containing the result of applying pf to this scala.Option's contained value, if this option is nonempty and pf is defined for that value. Returns None otherwise.

pf

the partial function.

returns

the result of applying pf to this scala.Option's value (if possible), or None.

Definition Classes
Option
Annotations
@inline()
Example:
    // Returns Some(HTTP) because the partial function covers the case.
    Some("http") collect {case "http" => "HTTP"}
    
    // Returns None because the partial function doesn't cover the case.
    Some("ftp") collect {case "http" => "HTTP"}
    
    // Returns None because the option is empty. There is no value to pass to the partial function.
    None collect {case value => value}

final def contains[A1 >: Nothing](elem: A1): Boolean

Tests whether the option contains a given value as an element.

This is equivalent to:

option match {
  case Some(x) => x == elem
  case None    => false
}
elem

the element to test.

returns

true if the option has an element that is equal (as determined by ==) to elem, false otherwise.

Definition Classes
Option
Example:
    // Returns true because Some instance contains string "something" which equals "something".
    Some("something") contains "something"
    
    // Returns false because "something" != "anything".
    Some("something") contains "anything"
    
    // Returns false when method called on None.
    None contains "anything"

final def eq(arg0: AnyRef): Boolean

Tests whether the argument (that) is a reference to the receiver object (this).

The eq method implements an equivalence relation on non-null instances of AnyRef, and has three additional properties:

    It is consistent: for any non-null instances x and y of type AnyRef, multiple invocations of x.eq(y) consistently returns true or consistently returns false.For any non-null instance x of type AnyRef, x.eq(null) and null.eq(x) returns false. null.eq(null) returns true.

When overriding the equals or hashCode methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2), they should be equal to each other (o1 == o2) and they should hash to the same value (o1.hashCode == o2.hashCode).

returns

true if the argument is a reference to the receiver object; false otherwise.

Definition Classes
AnyRef

def equals(arg0: AnyRef): Boolean

The equality method for reference types. Default implementation delegates to eq.

See also equals in scala.Any.

returns

true if the receiver object is equivalent to the argument; false otherwise.

Definition Classes
AnyRef → Any

final def exists(p: (Nothing) => Boolean): Boolean

Returns true if this option is nonempty and the predicate p returns true when applied to this scala.Option's value. Otherwise, returns false.

This is equivalent to:

option match {
  case Some(x) => p(x)
  case None    => false
}
p

the predicate to test

Definition Classes
Option
Annotations
@inline()

final def filter(p: (Nothing) => Boolean): Option[Nothing]

Returns this scala.Option if it is nonempty and applying the predicate p to this scala.Option's value returns true. Otherwise, return None.

This is equivalent to:

option match {
  case Some(x) if p(x) => Some(x)
  case _               => None
}
p

the predicate used for testing.

Definition Classes
Option
Annotations
@inline()

final def filterNot(p: (Nothing) => Boolean): Option[Nothing]

Returns this scala.Option if it is nonempty and applying the predicate p to this scala.Option's value returns false. Otherwise, return None.

This is equivalent to:

option match {
  case Some(x) if !p(x) => Some(x)
  case _                => None
}
p

the predicate used for testing.

Definition Classes
Option
Annotations
@inline()

def finalize(): Unit

Called by the garbage collector on the receiver object when there are no more references to the object.

The details of when and if the finalize method is invoked, as well as the interaction between finalize and non-local returns and exceptions, are all platform dependent.

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.Throwable])
Note

not specified by SLS as a member of AnyRef

final def flatMap[B](f: (Nothing) => Option[B]): Option[B]

Returns the result of applying f to this scala.Option's value if this scala.Option is nonempty. Returns None if this scala.Option is empty. Slightly different from map in that f is expected to return an scala.Option (which could be None).

This is equivalent to:

option match {
  case Some(x) => f(x)
  case None    => None
}
f

the function to apply

Definition Classes
Option
Annotations
@inline()
See also

map

foreach

def flatten[B](implicit ev: <:<[Nothing, Option[B]]): Option[B]

Returns the nested scala.Option value if it is nonempty. Otherwise, return None.

This is equivalent to:

option match {
  case Some(Some(b)) => Some(b)
  case _             => None
}
ev

an implicit conversion that asserts that the value is also an scala.Option.

Definition Classes
Option
Example:
    Some(Some("something")).flatten
See also

flatMap

final def fold[B](ifEmpty: => B)(f: (Nothing) => B): B

Returns the result of applying f to this scala.Option's value if the scala.Option is nonempty. Otherwise, evaluates expression ifEmpty.

This is equivalent to:

option match {
  case Some(x) => f(x)
  case None    => ifEmpty
}

This is also equivalent to:

option map f getOrElse ifEmpty
ifEmpty

the expression to evaluate if empty.

f

the function to apply if nonempty.

Definition Classes
Option
Annotations
@inline()

final def forall(p: (Nothing) => Boolean): Boolean

Returns true if this option is empty or the predicate p returns true when applied to this scala.Option's value.

This is equivalent to:

option match {
  case Some(x) => p(x)
  case None    => true
}
p

the predicate to test

Definition Classes
Option
Annotations
@inline()

final def foreach[U](f: (Nothing) => U): Unit

Apply the given procedure f to the option's value, if it is nonempty. Otherwise, do nothing.

This is equivalent to:

option match {
  case Some(x) => f(x)
  case None    => ()
}
f

the procedure to apply.

Definition Classes
Option
Annotations
@inline()
See also

map

flatMap

def get: Nothing

Returns the option's value.

This is equivalent to:

option match {
  case Some(x) => x
  case None    => throw new Exception
}
Definition Classes
NoneOption
Exceptions thrown

java.util.NoSuchElementException if the option is empty.

Note

The option must be nonempty.

final def getClass(): Class[_ <: AnyRef]

Returns the runtime class representation of the object.

returns

a class object corresponding to the runtime type of the receiver.

Definition Classes
AnyRef → Any
Annotations
@native()

final def getOrElse[B >: Nothing](default: => B): B

Returns the option's value if the option is nonempty, otherwise return the result of evaluating default.

This is equivalent to:

option match {
  case Some(x) => x
  case None    => default
}
default

the default expression.

Definition Classes
Option
Annotations
@inline()

final def isDefined: Boolean

Returns true if the option is an instance of scala.Some, false otherwise.

This is equivalent to:

option match {
  case Some(_) => true
  case None    => false
}
Definition Classes
Option

final def isEmpty: Boolean

Returns true if the option is None, false otherwise.

This is equivalent to:

option match {
  case Some(_) => false
  case None    => true
}
Definition Classes
Option

final def isInstanceOf[T0]: Boolean

Test whether the dynamic type of the receiver object is T0.

Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression 1.isInstanceOf[String] will return false, while the expression List(1).isInstanceOf[List[String]] will return true. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.

returns

true if the receiver object is an instance of erasure of type T0; false otherwise.

Definition Classes
Any

def iterator: Iterator[Nothing]

Returns a singleton iterator returning the scala.Option's value if it is nonempty, or an empty iterator if the option is empty.

Definition Classes
OptionIterableOnce

final def knownSize: Int

returns

The number of elements in this option, if it can be cheaply computed, -1 otherwise. Cheaply usually means: Not requiring a collection traversal.

Definition Classes
OptionIterableOnce

final def map[B](f: (Nothing) => B): Option[B]

Returns a scala.Some containing the result of applying f to this scala.Option's value if this scala.Option is nonempty. Otherwise return None.

This is equivalent to:

option match {
  case Some(x) => Some(f(x))
  case None    => None
}
f

the function to apply

Definition Classes
Option
Annotations
@inline()
Note

This is similar to flatMap except here, f does not need to wrap its result in an scala.Option.

See also

flatMap

foreach

final def ne(arg0: AnyRef): Boolean

Equivalent to !(this eq that).

returns

true if the argument is not a reference to the receiver object; false otherwise.

Definition Classes
AnyRef

final def nonEmpty: Boolean

Returns false if the option is None, true otherwise.

This is equivalent to:

option match {
  case Some(_) => true
  case None    => false
}
Definition Classes
Option
Note

Implemented here to avoid the implicit conversion to Iterable.

final def notify(): Unit

Wakes up a single thread that is waiting on the receiver object's monitor.

Definition Classes
AnyRef
Annotations
@native()
Note

not specified by SLS as a member of AnyRef

final def notifyAll(): Unit

Wakes up all threads that are waiting on the receiver object's monitor.

Definition Classes
AnyRef
Annotations
@native()
Note

not specified by SLS as a member of AnyRef

final def orElse[B >: Nothing](alternative: => Option[B]): Option[B]

Returns this scala.Option if it is nonempty, otherwise return the result of evaluating alternative.

This is equivalent to:

option match {
  case Some(x) => Some(x)
  case None    => alternative
}
alternative

the alternative expression.

Definition Classes
Option
Annotations
@inline()

final def orNull[A1 >: Nothing](implicit ev: <:<[Null, A1]): A1

Returns the option's value if it is nonempty, or null if it is empty.

Although the use of null is discouraged, code written to use scala.Option must often interface with code that expects and returns nulls.

This is equivalent to:

option match {
  case Some(x) => x
  case None    => null
}
Definition Classes
Option
Annotations
@inline()
Example:
    val initialText: Option[String] = getInitialText
    val textField = new JComponent(initialText.orNull,20)

def productElementName(n: Int): String

The name of the nth element of this product, 0-based. In the default implementation, an empty string.

n

the index of the element name to return

returns

the name of the specified element

Definition Classes
Product
Exceptions thrown

IndexOutOfBoundsException if the n is out of range(n < 0 || n >= productArity).

def productElementNames: Iterator[String]

An iterator over the names of all the elements of this product.

Definition Classes
Product

def stepper[S <: Stepper[_]](implicit shape: StepperShape[Nothing, S]): S

Returns a Stepper for the elements of this collection.

The Stepper enables creating a Java stream to operate on the collection, see scala.jdk.StreamConverters. For collections holding primitive values, the Stepper can be used as an iterator which doesn't box the elements.

The implicit StepperShape parameter defines the resulting Stepper type according to the element type of this collection.

    For collections of Int, Short, Byte or Char, an IntStepper is returnedFor collections of Double or Float, a DoubleStepper is returnedFor collections of Long a LongStepper is returnedFor any other element type, an AnyStepper is returned

Note that this method is overridden in subclasses and the return type is refined to S with EfficientSplit, for example IndexedSeqOps.stepper. For Steppers marked with scala.collection.Stepper.EfficientSplit, the converters in scala.jdk.StreamConverters allow creating parallel streams, whereas bare Steppers can be converted only to sequential streams.

Definition Classes
IterableOnce

final def synchronized[T0](arg0: => T0): T0

Definition Classes
AnyRef

final def toLeft[X](right: => X): Either[Nothing, X]

Returns a scala.util.Right containing the given argument right if this is empty, or a scala.util.Left containing this scala.Option's value if this scala.Option is nonempty.

This is equivalent to:

option match {
  case Some(x) => Left(x)
  case None    => Right(right)
}
right

the expression to evaluate and return if this is empty

Definition Classes
Option
Annotations
@inline()
See also

toRight

def toList: List[Nothing]

Returns a singleton list containing the scala.Option's value if it is nonempty, or the empty list if the scala.Option is empty.

This is equivalent to:

option match {
  case Some(x) => List(x)
  case None    => Nil
}
Definition Classes
Option

final def toRight[X](left: => X): Either[X, Nothing]

Returns a scala.util.Left containing the given argument left if this scala.Option is empty, or a scala.util.Right containing this scala.Option's value if this is nonempty.

This is equivalent to:

option match {
  case Some(x) => Right(x)
  case None    => Left(left)
}
left

the expression to evaluate and return if this is empty

Definition Classes
Option
Annotations
@inline()
See also

toLeft

final def unzip[A1, A2](implicit asPair: <:<[Nothing, (A1, A2)]): (Option[A1], Option[A2])

Converts an Option of a pair into an Option of the first element and an Option of the second element.

This is equivalent to:

option match {
  case Some((x, y)) => (Some(x), Some(y))
  case _            => (None,    None)
}
A1

the type of the first half of the element pair

A2

the type of the second half of the element pair

asPair

an implicit conversion which asserts that the element type of this Option is a pair.

returns

a pair of Options, containing, respectively, the first and second half of the element pair of this Option.

Definition Classes
Option

final def unzip3[A1, A2, A3](implicit asTriple: <:<[Nothing, (A1, A2, A3)]): (Option[A1], Option[A2], Option[A3])

Converts an Option of a triple into three Options, one containing the element from each position of the triple.

This is equivalent to:

option match {
  case Some((x, y, z)) => (Some(x), Some(y), Some(z))
  case _               => (None,    None,    None)
}
A1

the type of the first of three elements in the triple

A2

the type of the second of three elements in the triple

A3

the type of the third of three elements in the triple

asTriple

an implicit conversion which asserts that the element type of this Option is a triple.

returns

a triple of Options, containing, respectively, the first, second, and third elements from the element triple of this Option.

Definition Classes
Option

final def wait(): Unit

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])

final def wait(arg0: Long, arg1: Int): Unit

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])

final def wait(arg0: Long): Unit

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException]) @native()

final def withFilter(p: (Nothing) => Boolean): WithFilter

Necessary to keep scala.Option from being implicitly converted to scala.collection.Iterable in for comprehensions.

Definition Classes
Option
Annotations
@inline()

final def zip[A1 >: Nothing, B](that: Option[B]): Option[(A1, B)]

Returns a scala.Some formed from this option and another option by combining the corresponding elements in a pair. If either of the two options is empty, None is returned.

This is equivalent to:

(option1, option2) match {
  case (Some(x), Some(y)) => Some((x, y))
  case _                  => None
}
that

the options which is going to be zipped

Definition Classes
Option
Example:
    // Returns Some(("foo", "bar")) because both options are nonempty.
    Some("foo") zip Some("bar")
    
    // Returns None because `that` option is empty.
    Some("foo") zip None
    
    // Returns None because `this` option is empty.
    None zip Some("bar")

© 2002-2019 EPFL, with contributions from Lightbend.
Licensed under the Apache License, Version 2.0.
https://www.scala-lang.org/api/2.13.0/scala/None$.html