More interesting OO State

gistfile1.txt

  case class Node(id:Int)
  type SyncResponse = Either[String,List[Node]]
  
  class Network {
    var nodes: ListBuffer[Node] = ListBuffer.empty
    val rng = scala.util.Random
    /**
     * Removes dead nodes
     */
    def purge:SyncResponse = {
      val x = rng.nextInt(3)
      if((nodes.length % 5 == 1 )){  // a random error case
        nodes = ListBuffer.empty
        Left("************** PURGE KABOOM ****************")
      }else {
        val currentLength = nodes.length
        if(currentLength > x){
          val ret = nodes.toList.takeRight(x)
          (1 to x).foreach(e => nodes.remove(nodes.length - e))
          Right(ret)
        }else  Right(Nil)
      }
    }
    
    /**
     * Returns newly discovered nodes. A Side effect is that they are appended to nodes
     */
    def discover:SyncResponse = {
      val x = rng.nextInt(7)
//      if(true){
      if((nodes.length > 6  && (x % 4 == 1))){  // random error case
        Left("************** DISCOVER KABOOM ****************")
      }else {
        (1 to x).foreach(e => nodes.append(new Node(e)))
        Right(nodes.toList.takeRight(x))
      }
    }
    override def toString = "Network["+nodes.length+"]"

    def copy:Network = {
      val networkCopy = new Network
      networkCopy.nodes = nodes
      networkCopy
    }
  }


// lets make a referentially transparent version
  case class BetterNetwork(network:Network){

    def resyncTransparent:(BetterNetwork,SyncResponse)={
      val networkCopy = network.copy
      val newlyDiscovered = networkCopy.discover
      (BetterNetwork(networkCopy),newlyDiscovered)
    }

    def purgeTransparent:(BetterNetwork,SyncResponse)={
      val networkCopy = network.copy
      val newlypurged = networkCopy.purge
      (BetterNetwork(networkCopy),newlypurged)
    }
  }