Past exam of the year 1 of the computer science course of the University of Oxford / 2017 / Imperative programming (resit) / 6 / d / Solution

class VendingMachine[+A](val currentItem: Option[A], items: List[A]) {
  def this(items: List[A]) = this(None,items)
  def dispenseNext(): VendingMachine[A] = items match {
    case Nil =>
      if (currentItem.isDefined) new VendingMachine[A](None,Nil)
      else this
    case t :: ts => new VendingMachine[A](Some(t),ts)
  }
  def addAll[B >: A](newItems: List[B]): VendingMachine[B] =
    new VendingMachine[B](items ++ newItems)
}