Classes with cyclical references cannot be pickled or unpickled. They generate out of heap space errrors.

gistfile1.scala

import scala.pickling._
import json._

object Test extends App {
        val x = (new X).pickle
        println(x)
        x.unpickle[X]
}


class X {
        var y = new Y(this)
}


class Y(val x: X) {}