Question

I want to write a function for process sequence, like this:

def wrap[A >: Seq[_], B](seq : A)(f : () => B): Option[B] = {
    if(seq.isEmpty) None
    else Some(f())
}

But it doesn’t work
error:

error: value isEmpty is not a member of type parameter A

if(seq.isEmpty) None

What did I do wrong?

Answer 1

You don’t need to say anything about A at all. Just say that the first argument to wrap is a Seq, then you can pass in a Seq or any subclass thereof:

def wrap[B](seq : Seq[_])(f : () => B): Option[B] = {
    if(seq.isEmpty) None
    else Some(f())
}

wrap(List(1,2,3))(() => "hi") //returns Some("hi")