Option in Scala

Scala's answer to null: a value that is either there or admits it is not.

// Option is the type for "maybe a value", used where null would be.
val ports: Map[String, Int] = Map("http" -> 80, "ssh" -> 22)

// Map.get never throws: it answers Some(value) or None. getOrElse
// then covers the None case and hands back a plain Int.
def portOrDefault(service: String): Int = ports.get(service).getOrElse(8080)

// headOption is a safe head, returning None for an empty list.
def firstService(names: List[String]): Option[String] = names.headOption

// isDefined answers yes or no, and never reaches the value itself.
def isKnown(service: String): Boolean = ports.get(service).isDefined

// A match asks the same question but also binds what is inside.
def describe(service: String): String = ports.get(service) match
  case Some(port) => s"$service listens on $port"
  case None       => s"$service is not configured"

How it works

1. ports.get(service) hands back Some(port) or None instead of throwing.
2. getOrElse(8080) covers the missing case, and names.headOption is a head that is safe on an empty list.
3. isDefined answers yes or no, while the match also binds the value through case Some(port).

Keywords and builtins used here

• Boolean
• Int
• List
• Map
• None
• Option
• Some
• String
• case
• def
• describe
• firstService
• isKnown
• match
• portOrDefault
• val

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Step 1 of 3 in Option & Either, step 19 of 27 in Language basics.

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Option in other languages

• F#
• Rust