What is the easiest way to deeply clone (copy) a mutable Scala object?

Question

What is the easiest way to deeply clone (copy) a mutable Scala object?

Answer 1

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.

Answer 2

Since you want the easiest way to deep copy a Scala object and not the fastest, you can always serialize the object, provided that it's serializable, and then deserialize it back. The following code only runs when compiled, not in REPL.

def deepCopy[A](a: A)(implicit m: reflect.Manifest[A]): A =
  util.Marshal.load[A](util.Marshal.dump(a))

val o1 = new Something(...) // "Something" has to be serializable
val o2 = deepCopy(o1)