scala: assign null to primitive

Question

I am trying to assign null to a variable which is Double like this:

var foo = 0.0
foo = null

However, this gives an error that null cannot be implicitly converted to Double

So I do this instead:

foo = null.asInstanceOf[Double]

however the new value for foo is 0.0

How can I set the value to null?

Answer 1

You can't. Double is a value type, and you can only assign null to reference types. Instead, the Scala compiler replaces null with a default value of 0.0.

See default values in the SLS 4.2:

default  type
0        Int or one of its subrange types
0L       Long
0.0f     Float
0.0d     Double
false    Boolean

You cannot assign Java primitives to null, either. And while Scala's Double isn't truly a primitive (it is actually a class in Scala), it needs to compile down to double in Java byte code. Instead, you should use Option[Double] if you want to represent a value that is missing entirely, and try to never use null in Scala.