scala

Option

sealed abstract class Option[+A] extends Product with Serializable

Represents optional values. Instances of Option are either an instance of Some or the object None.

The most idiomatic way to use an Option instance is to treat it as a collection or monad and use map,flatMap, filter, or foreach:

 val name:Option[String] = request.getParameter("name")
 val upper = name map { _.trim } filter { _.length != 0 } map { _.toUpperCase }
 println(upper.getOrElse(""))

Note that this is equivalent to

 val upper = for {
   name <- request.getParameter("name")
   trimmed <- Some(name.trim)
   upper <- Some(trimmed.toUpperCase) if trimmed.length != 0
 } yield upper
 println(upper.getOrElse(""))

Because of how for comprehension works, if None is returned from request.getParameter, the entire expression results in None

This allows for sophisticated chaining of Option values without having to check for the existence of a value.

A less-idiomatic way to use Option values is via pattern matching:

 val nameMaybe = request.getParameter("name")
 nameMaybe match {
   case Some(name) => {
     println(name.trim.toUppercase)
   }
   case None => {
     println("No name value")
   }
 }
Self Type
Option[A]
Source
Option.scala
Version

1.1, 16/01/2007

Note

Many of the methods in here are duplicative with those in the Traversable hierarchy, but they are duplicated for a reason: the implicit conversion tends to leave one with an Iterable in situations where one could have retained an Option.

Linear Supertypes
Serializable, Serializable, Product, Equals, AnyRef, Any
Known Subclasses
Ordering
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Inherited
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  1. Option
  2. Serializable
  3. Serializable
  4. Product
  5. Equals
  6. AnyRef
  7. Any
Visibility
  1. Public
  2. All

Instance Constructors

  1. new Option()

Type Members

  1. 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.

Abstract Value Members

  1. abstract def canEqual(that: Any): Boolean

    A method that should be called from every well-designed equals method that is open to be overridden in a subclass.

    A method that should be called from every well-designed equals method that is open to be overridden in a subclass. See Programming in Scala, Chapter 28 for discussion and design.

    that

    the value being probed for possible equality

    returns

    true if this instance can possibly equal that, otherwise false

    Definition Classes
    Equals
  2. abstract def get: A

    Returns the option's value.

    Returns the option's value.

    Exceptions thrown
    Predef.NoSuchElementException

    if the option is empty.

    Note

    The option must be nonEmpty.

  3. abstract def isEmpty: Boolean

    Returns true if the option is None, false otherwise.

  4. abstract def productArity: Int

    The size of this product.

    The size of this product.

    returns

    for a product A(x_1, ..., x_k), returns k

    Definition Classes
    Product
  5. abstract def productElement(n: Int): Any

    The nth element of this product, 0-based.

    The nth element of this product, 0-based. In other words, for a product A(x_1, ..., x_k), returns x_(n+1) where 0 < n < k.

    n

    the index of the element to return

    returns

    the element n elements after the first element

    Definition Classes
    Product
    Exceptions thrown
    IndexOutOfBoundsException

Concrete Value Members

  1. final def !=(arg0: AnyRef): Boolean

    Definition Classes
    AnyRef
  2. final def !=(arg0: Any): Boolean

    Test two objects for inequality.

    Test two objects for inequality.

    returns

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

    Definition Classes
    Any
  3. final def ##(): Int

    Equivalent to x.hashCode except for boxed numeric types.

    Equivalent to x.hashCode except for boxed numeric types. 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.

    returns

    a hash value consistent with ==

    Definition Classes
    AnyRef → Any
  4. final def ==(arg0: AnyRef): Boolean

    Definition Classes
    AnyRef
  5. final def ==(arg0: Any): Boolean

    Test two objects for equality.

    Test two objects for equality.

    returns

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

    Definition Classes
    Any
  6. final def asInstanceOf[T0]: T0

    Cast the receiver object to be of type 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.

  7. def clone(): AnyRef

    Create a copy of the receiver object.

    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[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws()
    Note

    not specified by SLS as a member of AnyRef

  8. def collect[B](pf: PartialFunction[A, B]): Option[B]

    Returns a Some containing the result of applying pf to this Option's contained value, if this option is nonempty and pf is defined for that value.

    Returns a Some containing the result of applying pf to this 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 Option's value (if possible), or None.

  9. final def eq(arg0: AnyRef): Boolean

    Tests whether the argument (arg0) is a reference to the receiver object (this).

    Tests whether the argument (arg0) 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
  10. def equals(arg0: Any): Boolean

    The equality method for reference types.

    The equality method for reference types. See equals in Any.

    returns

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

    Definition Classes
    AnyRef → Any
  11. final def exists(p: (A) ⇒ Boolean): Boolean

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

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

    p

    the predicate to test

    Annotations
    @inline()
  12. final def filter(p: (A) ⇒ Boolean): Option[A]

    Returns this Option if it is nonempty and applying the predicate p to this Option's value returns true.

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

    p

    the predicate used for testing.

    Annotations
    @inline()
  13. final def filterNot(p: (A) ⇒ Boolean): Option[A]

    Returns this Option if it is nonempty and applying the predicate p to this Option's value returns false.

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

    p

    the predicate used for testing.

    Annotations
    @inline()
  14. def finalize(): Unit

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

    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[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws()
    Note

    not specified by SLS as a member of AnyRef

  15. final def flatMap[B](f: (A) ⇒ Option[B]): Option[B]

    Returns the result of applying f to this Option's value if this Option is nonempty.

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

    f

    the function to apply

    Annotations
    @inline()
    See also

    foreach

    ,

    map

  16. final def foreach[U](f: (A) ⇒ U): Unit

    Apply the given procedure f to the option's value, if it is nonempty.

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

    f

    the procedure to apply.

    Annotations
    @inline()
    See also

    flatMap

    ,

    map

  17. final def getClass(): java.lang.Class[_]

    A representation that corresponds to the dynamic class of the receiver object.

    A representation that corresponds to the dynamic class of the receiver object.

    The nature of the representation is platform dependent.

    returns

    a representation that corresponds to the dynamic class of the receiver object.

    Definition Classes
    AnyRef → Any
    Note

    not specified by SLS as a member of AnyRef

  18. final def getOrElse[B >: A](default: ⇒ B): B

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

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

    default

    the default expression.

    Annotations
    @inline()
  19. def hashCode(): Int

    The hashCode method for reference types.

    The hashCode method for reference types. See hashCode in Any.

    returns

    the hash code value for this object.

    Definition Classes
    AnyRef → Any
  20. def isDefined: Boolean

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

  21. final def isInstanceOf[T0]: Boolean

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

    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
  22. def iterator: Iterator[A]

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

  23. final def map[B](f: (A) ⇒ B): Option[B]

    Returns a Some containing the result of applying f to this Option's value if this Option is nonempty.

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

    f

    the function to apply

    Annotations
    @inline()
    Note

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

    See also

    foreach

    ,

    flatMap

  24. final def ne(arg0: AnyRef): Boolean

    Equivalent to !(this eq that).

    Equivalent to !(this eq that).

    returns

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

    Definition Classes
    AnyRef
  25. final def notify(): Unit

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

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

    Definition Classes
    AnyRef
    Note

    not specified by SLS as a member of AnyRef

  26. final def notifyAll(): Unit

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

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

    Definition Classes
    AnyRef
    Note

    not specified by SLS as a member of AnyRef

  27. final def orElse[B >: A](alternative: ⇒ Option[B]): Option[B]

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

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

    alternative

    the alternative expression.

    Annotations
    @inline()
  28. final def orNull[A1 >: A](implicit ev: <:<[Null, A1]): A1

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

    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 Option must often interface with code that expects and returns nulls.

    Annotations
    @inline()
    Example:
    1. val initalText: Option[String] = getInitialText
      val textField = new JComponent(initalText.orNull,20)
      
  29. def productIterator: Iterator[Any]

    An iterator over all the elements of this product.

    An iterator over all the elements of this product.

    returns

    in the default implementation, an Iterator[Any]

    Definition Classes
    Product
  30. def productPrefix: String

    A string used in the toString methods of derived classes.

    A string used in the toString methods of derived classes. Implementations may override this method to prepend a string prefix to the result of toString methods.

    returns

    in the default implementation, the empty string

    Definition Classes
    Product
  31. final def synchronized[T0](arg0: ⇒ T0): T0

    Definition Classes
    AnyRef
  32. final def toLeft[X](right: ⇒ X): Product with Serializable with Either[A, X]

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

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

    right

    the expression to evaluate and return if this is empty

    Annotations
    @inline()
    See also

    toRight

  33. def toList: List[A]

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

  34. final def toRight[X](left: ⇒ X): Product with Serializable with Either[X, A]

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

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

    left

    the expression to evaluate and return if this is empty

    Annotations
    @inline()
    See also

    toLeft

  35. def toString(): String

    Creates a String representation of this object.

    Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.

    returns

    a String representation of the object.

    Definition Classes
    AnyRef → Any
  36. final def wait(): Unit

    Definition Classes
    AnyRef
    Annotations
    @throws()
  37. final def wait(arg0: Long, arg1: Int): Unit

    Definition Classes
    AnyRef
    Annotations
    @throws()
  38. final def wait(arg0: Long): Unit

    Definition Classes
    AnyRef
    Annotations
    @throws()
  39. def withFilter(p: (A) ⇒ Boolean): WithFilter

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

Deprecated Value Members

  1. def productElements: Iterator[Any]

    Definition Classes
    Product
    Annotations
    @deprecated
    Deprecated

    (Since version 2.8.0) use productIterator instead

Inherited from Serializable

Inherited from Serializable

Inherited from Product

Inherited from Equals

Inherited from AnyRef

Inherited from Any