scalasingleton-type

Specifying type of a Case Object in Either

If I have a object as follows:

case object Foo

and I try to create a value like this

Either[Foo, B]

I get a compile error saying that Foo cannot be found. But if I do this:

Either[Foo.type, B]

It compiles. My question is if this correct to do this?

Solution

  • Whenever you want to declare the type of an object in Scala you have to declare it like YourObject.type.

    The reason is simple, as YourObject is already the instance. So .type is the way you have to declare the Type of an Object (Singleton) in Scala.

    Here an example:

    object YourObject

def doit(obj: YourObject.type) = {}

def doitEventually(obj: Option[YourObject.type]) = {}


doit(YourObject)
doitEventually(Some(YourObject))

    I couldn't find the according documentation, so maybe someone can help out with that.

    The Specification is here: singleton-types (as mentioned by Mojo in the comments)