Scala Some v. Option

Question

What\'s the difference between Some and Option?

scala> Some(true)
res2: Some[Boolean] = Some(true)

scala> val x: Option[Boolean]         


        

Answer 1

Well, Some extends Option, so it inherits everything except get and isEmpty (and some other methods implemented by a case class).

The companion object of Option has a special apply method for dealing with null:

def apply[A](x: A): Option[A] = if (x == null) None else Some(x)

But Some.apply is just the standard apply method generated for a case class.

Some(null) will compile in some circumstances, but it has type Some[Null] (or Option[Null]), which can only be assigned when the type argument of Option is a reference type.

scala> val a = Some(null)
a: Some[Null] = Some(null)

scala> val b: Option[String] = Some(null)
b: Option[String] = Some(null)

You're trying to assign a Some[Null] to an Option[Boolean], but a Null is not a sub-type of Boolean, because Boolean is a value type (primitive underneath) and cannot hold a value of null.