Leaking mutable state into a future..

FutureLeak.scala

import akka.actor._
import akka.dispatch._
import akka.pattern.pipe

trait StuffService {
  type Stuff
  def doStuff :Future[Stuff]
}

case object DoStuff

class LeakyLeaksalot( service :StuffService ) extends Actor {
  import StuffService._

  var currentStuff :List[Stuff] = Nil

  def receive = {
    case DoStuff => // bad
      service.doStuff.map { sender ! _ }
   
    case DoStuff => // better
      val replyTo = sender
      service.doStuff.map { replyTo ! _ }
  
    case DoStuff => // best
      service doStuff pipeTo sender

   case DoStuff => // very bad. local mutable var leaked into future block
     service doStuff map { currentStuff :+ _ } 
  }
}