Banker's Queue Implementation

bankersQueue.sc

object queuesBankers {
  import BankersQueue._

  case class BankersQueue[+A](sizeFront: Int, front: Stream[A], sizeRear: Int, rear: Stream[A]) {
    def enqueue[B >: A](b: B) =
      check(BankersQueue(sizeFront,front, sizeRear + 1, b #:: rear))

    def dequeue = front match {
      case h #:: t => {
        val remaining = BankersQueue(sizeFront - 1, t, sizeRear, rear)
        (h, check(remaining))
      }
      case _ => throw new NoSuchElementException()
    }
  }

  object BankersQueue {
    def check[A](q: BankersQueue[A]) = {
      if (q.sizeFront >= q.sizeRear) q
      else {
        val newFrontSize = q.sizeFront + q.sizeRear
        val newFront = q.front ++ q.rear.reverse

        BankersQueue(newFrontSize, newFront, 0, Stream[A]())
      }
    }
  }

  val bq = BankersQueue[Int](0, Stream(), 0, Stream())
    .enqueue(1)
    .enqueue(2)
    .enqueue(3)
    .enqueue(4)
    .enqueue(5)

  val (next, bq2) = bq.dequeue
  val (next1, bq3) = bq2.dequeue
  val bq4 = bq3.enqueue(10)
  val (next2, bq5) = bq4.dequeue

}