stackable trait pattern

gistfile1.scala

// stackable trait pattern
// http://www.artima.com/scalazine/articles/stackable_trait_pattern.html

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

import scala.collection.mutable.ArrayBuffer

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(x * 2)
}

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

trait Filtering extends IntQueue {
  abstract override def put(x: Int) = if (x >= 0) super.put(x)
}