Options in Scala

A quick tour

Option[Introduction]

An Option represents an optional value through either:

• An instance of Some[Type]• The object None

An option can be typed by:

• Option[Type]

Option[Inheritance]

 

Option[Null] 

Options allow for null checking, but this misses the point and conciseness. 

val optionalValue = Some[3]

val value = if (optionalValue.isDefined)    optionalValue.get

Options give more than preventing NullPointerExceptions.

Option[PatternMatching]

A more interesting, but still not quite idiomatic approach is pattern matching:

val optionalValue = Some[3]

optionalValue match {    case Some(number) => // its a number!    case _ => // anything else}

Option[Default]

val optionalValue = Some[3]

val value = optionalValue getOrElse 0

Option[Idiomatic]

Option[+A] can be considered to be a subtype of Traversable with either one or zero elements.

This allows use of collection based functions like map and filter.

 

Option[Transformations]

val personOpt: Option[Person] = findPerson()

val deptNameOption: Option[String] =     personOpt map { _.department } map { _.name }

val deptName = deptNameOption getOrElse ""

Option[ListComprehension]

val personOption: Option[Person] = findPerson()

val deptNameOption = for {    person <- personOption    department <- person.department    name <- department.name if name != "Engineering"} yield name

val deptName = deptNameOption getOrElse ""

List[Question]