Question

What the difference between List.empty, List() and new List()? When should I use which?

Answer 1

First of all, new List() won’t work, since the List class is abstract. The other two options are defined as follows in the List object:

override def empty[A]: List[A] = Nil
override def apply[A](xs: A*): List[A] = xs.toList

I.e., they’re essentially equivalent, so it’s mostly a matter of style. I prefer to use empty because I find it clearer, and it cuts down on parentheses.