Scala: Compare types

Question

I want to define a function that could compare two class types. I have defined two different classes:

abstract class Task
case class DefinedTask(id: Long) extends Task
case class EmptyTask() extends Task  

Then I have a function that returns an object of type Task, that could be either DefinedTask or EmptyTask.

Now, what I'd like to do is to have a function that identifies if this object is a DefinedTask or just an EmptyTask. The problem would be simple, I'd use pattern matching. But I want to generalize it because multiple classes go with this Defined/Empty pattern.

What I'd tried so far is:

def makeReturned[T: Manifest, U: Manifest](obj: T)(u: U)(f: T => Value) = 
   if(manifest[U] equals manifest[T]) f(obj) else
     throw new IllegalArgumentException()
}
//call to it
makeReturned(task)(DefinedTask)(makeTask)

U is always DefinedTask, T could be either DefinedTask or EmptyTask, but it is returned as Task.

manifest[U].erasure.toString //"class DefinedTask$"
manifest[T].erasure.toString //"class Task"  

Which is right from the compiler's stand point but it's not for me. So, my question is how could I compare them in a way that would give me what I want?

Answer 1

It looks like you want run-time, not compile-time checking. So I think you mean

def makeReturned[U <: Task, T <: Task](obj: T)(u: U)(f: T => Value) = {
  if (obj.getClass.isInstance(u.getClass)) f(obj)
  else throw new IllegalArgumentException
}

or something like that. Look at the methods on java.lang.Class and pick the one that does what you want.