I would strongly advise not to inherit from a case class. It has surprising effects on equals and hashCode, and has been deprecated in Scala 2.8.
Instead, define x in a trait or an abstract class.
scala> trait A { val x: Int }
defined trait A
scala> case class B(val x: Int, y: Int) extends A
defined class B
http://www.scala-lang.org/node/3289
http://www.scala-lang.org/node/1582
E. Tempero, J. Noble, und H. Melton. ECOOP 2008 European Conf. on Object-Oriented Programming, Volume 5142 von Lecture Notes in Computer Science, Seite 667--691. Springer Berlin / Heidelberg, (2008)
H. Frank. ADBIS (Short Papers), Seite 148--154. Institute of Informatics, Faculty of Electrical Engineering and Computer Science, Smetanova 17, IS-2000 Maribor, Slovenia, (1999)
H. Frank. ADBIS (Short Papers), Seite 148--154. Institute of Informatics, Faculty of Electrical Engineering and Computer Science, Smetanova 17, IS-2000 Maribor, Slovenia, (1999)