Object scala.None
object None extends Option[Nothing] with Product with Serializable
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 typeT0
.
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.
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), orNone
.
- Definition Classes
- Option
- Annotations
- @inline()
// 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==
) toelem
,false
otherwise.
- Definition Classes
- Option
// 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
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.
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.
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.
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
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
- See also
flatMap
Some(Some("something")).flatten
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.
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
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.
def get: Nothing
Returns the option's value.
This is equivalent to:
option match { case Some(x) => x case None => throw new Exception }
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.
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.
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 typeT0
;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
- Option → IterableOnce
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
- Option → IterableOnce
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.
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 }
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 then
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 returnedNote 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
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
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
final def withFilter(p: (Nothing) => Boolean): WithFilter
Necessary to keep scala.Option from being implicitly converted to scala.collection.Iterable in for
comprehensions.
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
// 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
This case object represents non-existent values.
1.0