Pass by reference for Scala

PassByReference.scala

// 'out' and 'inout' arguments for scala

object BasicExample {
  // out param
  def set(newvalue: Int, x: Int => Unit) { x(newvalue) }
  // inout param
  def inc(amount: Int, x: (Int, Int => Unit)) { x._2(x._1 + amount) }
}

// with wrapper classes
class OutP[T](set: T => Unit) {
  def update(newvalue: T) = set(newvalue)
}
object OutP {
  def apply[T](set: T => Unit) = new OutP(set)
}
class InOutP[T](get: T, set: T => Unit) extends OutP[T](set) {
  def apply() = get
}
object InOutP {
  def apply[T](get: T, set: T => Unit) = new InOutP[T](get, set)
}

object BetterExample {
  def set(newvalue: Int, x: OutP[Int]) { x() = newvalue }
  def inc(amount: Int, x: InOutP[Int]) = { x() += amount }
}

object Demo extends Application {
  var x = 0
  println("BasicExample x = " + x)
  BasicExample.set(9, x=_)
  println("x = " + x)
  BasicExample.inc(2, (x,x=_))
  println("x = " + x)

  x = 0
  println("Better x = " + x)
  BetterExample.set(9, OutP(x=_))
  println("x = " + x)
  BetterExample.inc(2, InOutP(x,x=_))
  println("x = " + x)
}