static - What replaces class variables in scala?

Question

In Java I sometimes use class variables to assign a unique ID to each new instance. I do something like

public class Foo {

  private static long nextId = 0;

  public final long id;

  public Foo() {
    id = nextId;
    nextId++;
  }

  [...]

}

How can I do this in Scala?

Answer 1

Variables on the companion object:

object Foo{
    private var current = 0
    private def inc = {current += 1; current}
}

class Foo{
    val i = Foo.inc
    println(i)
}