在Akka Streams中将Sink转换为Graph（SinkShape）？

Question

I have something like this:

implicit val system = ActorSystem("actorSystem")
implicit val materializer = ActorMaterializer()

val (ref: ActorRef, publisher: Publisher[(String, String, String)]) =
  Source.actorRef[(String, String, String)](bufferSize = 1000, OverflowStrategy.fail)
    .toMat(transferFTP(_))(Keep.both)
    .run()

def transferFTP(data: (String, String, String)): Sink[ByteString, Future[IOResult]] = {
  // ...
}

In every example I have read, toMat() takes a Sink as a parameter, but the compiler expects Graph[SinkShape[(String,String,String)], NotInferedMat2] .

Answer 1

toMat does take a Sink . A Sink[(String, String, String), _] is a Graph[SinkShape[(String, String, String)], _] (in other words, the former is a subclass of the latter). One of the problems is that you're passing in a Sink[ByteString, _] instead. Also, you're expecting a Publisher[(String, String, String)] when the materialized value of your Sink is a Future[IOResult] .

The following is an example in which the types align, thus making the compiler happy:

val tupleToByteString: ((String, String, String)) => ByteString = ???

val transferFTP: Sink[ByteString, Future[IOResult]] = ???

val (ref: ActorRef, sink: Future[IOResult]) =
  Source.actorRef[(String, String, String)](bufferSize = 1000, OverflowStrategy.fail)
    .via(Flow.fromFunction(tupleToByteString)) // alternatively: .map(tupleToByteString)
    .toMat(transferFTP)(Keep.both)
    .run()