Initialize Scala variables with Option, None, and Some (not null)

Summary: How to properly use the Scala Option/Some/None idiom to initialize empty var fields — and specifically how not to use null values for the same purpose.

When you get started in the Scala world, you quickly learn that null values are a bad thing. Scala makes it easy to replace null values with something better, and that something better is what I call the Option/Some/None pattern (or idiom).

Totally avoiding null values, here's the correct Scala, idiomatic way of initializing, setting, and then accessing a variable:

// 1) initialize with Option and None
var firstName = None: Option[String]

// 2) set the value with Some
firstName = Some("Al")

// 3) access the value, typically with getOrElse
println(firstName)
println(firstName.getOrElse("No name given"))

This is shown in the Scala REPL:

scala> var firstName = None: Option[String]
firstName: Option[String] = None

scala> firstName = Some("Al")
firstName: Option[String] = Some(Al)

scala> println(firstName)
Some(Al)

scala> println(firstName.getOrElse("No name given"))
Al

Of course an assumption in this code is that the field firstName has no initial value.

Note that the Java approach would be to set firstName as either a null value, or in the case of a String, perhaps an empty string (""). In Scala we avoid both of those approaches and use the Option/Some/None pattern, as shown.

Note: If you simply think of null as being evil and never allow a null value in your code, the Option/Some/None pattern will quickly become your good friend.

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