Usages of Null / Nothing / Unit in Scala

Question

I\'ve just read: http://oldfashionedsoftware.com/2008/08/20/a-post-about-nothing/

As far as I understand, Null is a trait and its only instance is

Answer 1

Here's an example of Nothing from scala.predef:

  def ??? : Nothing = throw new NotImplementedError

In case you're unfamiliar (and search engines can't search on it) ??? is Scala's placeholder function for anything that hasn't been implemented yet. Just like Kotlin's TODO.

You can use the same trick when creating mock objects: override unused methods with a custom notUsed method. The advantage of not using ??? is that you won't get compile warnings for things you never intend to implement.