is this future map scala syntax good?

Question

I'm new to scala and have been working to understand the syntax so that I can be more efficient. How does this look in terms of functional syntax and scala idioms?

In particular, I'd like to know if this is a good way of handling futures. I'm aware of onComplete, onSuccess, etc..., matching but I had trouble getting a return value back out. map seemed like the right approach here.

object Application extends Controller with securesocial.core.SecureSocial {
 val inboxSlurper = Akka.system.actorOf(Props[InboxSlurper], name = "inboxSlurper")
 def index = SecuredAction.async {
 implicit request =>
 implicit val timeout = Timeout(10 seconds)
 val user: User = request.user.asInstanceOf[User]
 val f = inboxSlurper.ask(
 OauthIdentity(
 user.email.get,
 user.oAuth2Info.get.accessToken))
 f flatMap { reply =>
 val emailFeed = reply.asInstanceOf[Enumerator[Message]]
 val iter = Iteratee.fold[Message, String]("")((result, msg) => result + msg.getSubject())
 emailFeed |>>> iter
 } map { str =>
 Logger.debug(str);
 val subj = "Subject: %s".format(str)
 Ok(views.html.index(subj))
 }
 }
}

Answer 1

Future "callbacks" can be simplified by using the for comprehension to compose futures. More information can be found here http://docs.scala-lang.org/overviews/core/futures.html#functional_composition_and_forcomprehensions

I'm not a Scala expert, but this is how i would replace the flatMap and map with a for

object Application extends Controller with securesocial.core.SecureSocial {
 val inboxSlurper = Akka.system.actorOf(Props[InboxSlurper], name = "inboxSlurper")
 def index = SecuredAction.async { implicit request =>
 implicit val timeout = Timeout(10 seconds)
 val user = request.user.asInstanceOf[User]
 for {
 emailFeed <- (inboxSlurper ? OauthIdentity(user.email.get, user.oAuth2Info.get.accessToken))).mapTo[Enumerator[Message]]
 str <- emailFeed |>>> Iteratee.fold[Message, String]("")((result, msg) => result + msg.getSubject())
 } yield Ok(views.html.index("Subject: %s".format(str)))
 }
}

The example demonstrates the sequential composition of futures, str will be calculated when emailFeed has retrieved the data for the inboxSlurper actor. After all futures have been completed then a result can be returned with yield.

Because everything is a expression in Scala for {} yield Ok() will be returned as result for the Action, which is a Future[SimpleResult].