The ask-pattern implements the initiator side of a request–reply protocol.
The party that asks may be within or without an Actor, since the
implementation will fabricate a (hidden)
ActorRef that is bound to a
Promise. This ActorRef will need to be injected in the
message that is sent to the target Actor in order to function as a reply-to
address, therefore the argument to the ask /
?
operator is not the message itself but a function that given the reply-to
address will create the message.
case class Request(msg: String, replyTo: ActorRef[Reply])
case class Reply(msg: String)
implicit val timeout = Timeout(3.seconds)
val target: ActorRef[Request] = ...
val f: Future[Reply] = target ? (Request("hello", _))