scala

# Option

#### 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")
       }
     }

Attributes
  sealed abstract
Self Type
  Option[A]
Source
  Option.scala
Version

  1.1, 16/01/2007

Linear Supertypes
Serializable, Serializable, Product, Equals, AnyRef, Any
Known Subclasses
None, Some
Ordering

1. Alphabetic
2. By inheritance

Inherited

1. Hide All
2. Show all

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. #### 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

   Attributes
     abstract
   Definition Classes
     Equals

2. #### def get : A

   Returns the option's value.

   Returns the option's value.

   Attributes
     abstract

3. #### def isEmpty : Boolean

   Returns true if the option is `None`, false otherwise.

   Returns true if the option is `None`, false otherwise.

   Attributes
     abstract

4. #### def productArity : Int

   The size of this product.

   The size of this product.

   returns

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

   Attributes
     abstract
   Definition Classes
     Product

5. #### 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

   Attributes
     abstract
   Definition Classes
     Product

### Concrete Value Members

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

   Attributes
     final
   Definition Classes
     AnyRef

2. #### def != (arg0: Any): Boolean

   Test two objects for inequality.

   Test two objects for inequality.

   returns

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

   Attributes
     final
   Definition Classes
     Any

3. #### 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 ==

   Attributes
     final
   Definition Classes
     AnyRef → Any

4. #### def == (arg0: AnyRef): Boolean

   Attributes
     final
   Definition Classes
     AnyRef

5. #### 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.

   Attributes
     final
   Definition Classes
     Any

6. #### 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.

   Attributes
     final
   Definition Classes
     Any

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()

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. #### 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.

   Attributes
     final
   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. #### 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

    Attributes
      final
    Annotations
      @inline()

12. #### 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.

    Attributes
      final
    Annotations
      @inline()

13. #### 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.

    Attributes
      final
    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()

15. #### 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

    Attributes
      final
    Annotations
      @inline()
    See also

      foreach

      ,

      map

16. #### 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.

    Attributes
      final
    Annotations
      @inline()
    See also

      flatMap

      ,

      map

17. #### 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.

    Attributes
      final
    Definition Classes
      AnyRef → Any

18. #### 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.

    Attributes
      final
    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. #### 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.

    Attributes
      final
    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. #### 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

    Attributes
      final
    Annotations
      @inline()
    See also

      foreach

      ,

      flatMap

24. #### 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.

    Attributes
      final
    Definition Classes
      AnyRef

25. #### 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.

    Attributes
      final
    Definition Classes
      AnyRef

26. #### 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.

    Attributes
      final
    Definition Classes
      AnyRef

27. #### 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.

    Attributes
      final
    Annotations
      @inline()

28. #### 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.

    Attributes
      final
    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. #### def synchronized [T0] (arg0: ⇒ T0): T0

    Attributes
      final
    Definition Classes
      AnyRef

32. #### 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

    Attributes
      final
    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. #### 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

    Attributes
      final
    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. #### def wait (): Unit

    Attributes
      final
    Definition Classes
      AnyRef
    Annotations
      @throws()

37. #### def wait (arg0: Long, arg1: Int): Unit

    Attributes
      final
    Definition Classes
      AnyRef
    Annotations
      @throws()

38. #### def wait (arg0: Long): Unit

    Attributes
      final
    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

     use productIterator instead

### Inherited from Serializable

### Inherited from Product

### Inherited from Equals

### Inherited from AnyRef

### Inherited from Any