What is the easiest way to deeply clone (copy) a mutable Scala object?
A Java-specific solution (which should work great in Scala too), is the Cloner library. It's fast, easy, deeply clones objects based on fields (using reflection), and is smart enough not to clone known immutable objects (like String, Integer, etc.). Finally, you can register custom immutable objects so it won't clone them either.
I highly recommend it.