stacked modification

gistfile1.scala

import scala.collection.mutable.ArrayBuffer

abstract class IntQueue {
  def get(): Int
  def put(x:Int)
}

class BasicIntQueue extends IntQueue {
  private val buf = new ArrayBuffer[Int]
  def get() = buf.remove(0)
  def put(x:Int) {buf += x }
}

trait Doubling extends IntQueue {
  abstract override def put(x:Int) { super.put(2 * x) }
}

trait Incrementing extends IntQueue {
  abstract override def put(x:Int) { super.put(x + 1) }
}

----------------------
run:
scala> val queue1 = new BasicIntQueue with Doubling with Incrementing
queue1: BasicIntQueue with Doubling with Incrementing = $anon$1@7595edfe

scala> val queue2 = new BasicIntQueue with Incrementing with Doubling
queue2: BasicIntQueue with Incrementing with Doubling = $anon$1@7fbcac12

scala> queue1.put(10)

scala> queue1.get
res12: Int = 22

scala> queue2.put(10)

scala> queue2.get
res14: Int = 21