import scala.collection.mutable.ArrayBuffer

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

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

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

class MyIntQueue extends BaseIntQueue with Doubling

val queue = new MyIntQueue
queue.put(10)
queue.put(20)
println(queue.get)
println(queue.get)