karol_dziachan

covariant Queue Scala

Jan 9th, 2021
869
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  1. class MyQueue[+T](private val rep: List[T] = Nil){
  2.  
  3.   def enqueue[S >: T](elem: S) =  new MyQueue[S](elem :: rep)
  4.  
  5.    def dequeue : MyQueue[T] = rep match{
  6.       case _::t => new MyQueue[T](t)
  7.       case Nil => throw new UnderflowException("Empty queue")
  8.     }
  9.      def isEmpty = rep == Nil
  10.  
  11.     def first: T = rep match{
  12.       case h::t => h
  13.       case Nil => throw new UnderflowException("Empty queue")
  14.     }
  15.   }
  16.  
  17. object MyQueue {
  18.   def apply[T](xs: T*): MyQueue[T] = new MyQueue[T](xs.toList)
  19.  
  20.   def empty[T]: MyQueue[T] = new MyQueue[T](Nil)
  21.  
  22. }
  23.  
  24. object Tester{
  25.   def main (args: Array[String]): Unit = {
  26.     val queue = MyQueue.empty
  27.     val queue1 = MyQueue()
  28.     val queue2 = MyQueue('a', 'b', 'c')
  29.     val queue3 = new MyQueue
  30.  
  31.     println(queue.enqueue(1).enqueue(2).dequeue.first)
  32.     println(queue1.enqueue("first").enqueue("A").dequeue.first)
  33.     println(queue2.dequeue.first)
  34.     println(queue3.enqueue(1).enqueue(2).dequeue.first)
  35. }
  36. }
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