Fixed a critical mistake

Erroneously used functional actor for mutable state.
Changed actor style to OO from functional.
Experimented with ask pattern to get final result

.gitignore

@@ -0,0 +1,2 @@
+.ammonite
+.metals

ActorDemo.sc

@@ -13,35 +13,47 @@ import akka.util.Timeout
 import scala.concurrent.duration._
 import akka.actor.typed.scaladsl.AskPattern._
 import scala.concurrent.ExecutionContext.Implicits.global
+import akka.actor.typed.scaladsl.AbstractBehavior
+import akka.actor.typed.scaladsl.ActorContext
+import scala.util.Success
+import scala.util.Failure
+import scala.concurrent.Await
+import scala.concurrent.Future
 
 object CounterActor {
+  final case class CounterResult(count: Int)
+
   sealed trait Command
   final case object IncCount extends Command
-  final case class CounterResult(count: Int)
-  final case class GetResult(sender: ActorRef[RootActor.Command])
-      extends Command
-
-  var counter = 0
+  final case class GetResult(sender: ActorRef[CounterResult]) extends Command
 
   def apply(): Behavior[Command] =
-    Behaviors.receive { (context, command) =>
-      command match {
-        case IncCount => counter += 1
+    Behaviors.setup(ctx => new CounterActor(ctx))
+
+  private class CounterActor(context: ActorContext[Command])
+      extends AbstractBehavior[Command](context) {
+    private var counter = 0 // encapsulated mutable state
+    override def onMessage(msg: Command): Behavior[Command] = {
+      msg match {
+        case IncCount =>
+          counter += 1
+          Behaviors.same
         case GetResult(sender) =>
           context.log.info(s"Value of counter is $counter");
-          sender ! RootActor.Reply(counter)
-      }
-
+          sender ! CounterResult(counter)
           Behaviors.same
       }
+    }
+  }
 
 }
 
 object RootActor {
   sealed trait Command
-  case class Reply[T](reply: T) extends Command
-  case object Begin extends Command
-  case object GetResult extends Command
+  final case class Reply[T](reply: T) extends Command
+  final case object Begin extends Command
+  final case class GetResult(repyTo: ActorRef[CounterActor.CounterResult])
+      extends Command
 
   implicit val timeout: Timeout = 3.seconds
 
@@ -63,10 +75,11 @@ object RootActor {
             counterActor ! CounterActor.IncCount
             counterActor ! CounterActor.IncCount
 
-          case GetResult =>
+          case GetResult(replyTo) =>
             counterActor ! CounterActor.GetResult(
-              context.self
+              replyTo
             )
+
         }
 
         Behaviors.same
@@ -77,13 +90,15 @@ object RootActor {
 
 @main
 def main() = {
-  implicit val rootActor =
+  implicit val system =
     ActorSystem(RootActor(), "TestActors")
 
   implicit val timeout: Timeout = 3.seconds
 
-  rootActor ! RootActor.Begin
-  rootActor ! RootActor.GetResult
+  system ! RootActor.Begin
+  // system ! RootActor.GetResult
 
-  Thread.sleep(1000)
+  val x: Future[CounterActor.CounterResult] =
+    system ? (ref => RootActor.GetResult(ref))
+  Await.result(x, 1.second)
 }

README.md

@@ -3,15 +3,15 @@
 An experiment to see how the actor model can be used to synchronize / encapsulate mutable state without the use of locks.
 
 ## Usage
+
 ```bash
 ./ActorsDemo.sc
 ```
 
 Sample output:
-```
-22:11:47.473 [TestActors-akka.actor.default-dispatcher-3] INFO ammonite.$file.ActorDemo$RootActor$ - --- Beginning ---
 
-22:11:47.475 [TestActors-akka.actor.default-dispatcher-6] INFO ammonite.$file.ActorDemo$CounterActor$ - Value of counter is 5
-
-22:11:47.475 [TestActors-akka.actor.default-dispatcher-3] INFO ammonite.$file.ActorDemo$RootActor$ - Received message Reply(5)
+```
+13:02:58.966 [TestActors-akka.actor.default-dispatcher-3] INFO ammonite.$file.AkkaActorsDemo.ActorDemo$RootActor$ - --- Beginning ---
+13:02:58.967 [TestActors-akka.actor.default-dispatcher-5] INFO ammonite.$file.AkkaActorsDemo.ActorDemo$CounterActor$CounterActor - Value of counter is 5
+CounterResult(5)
 ```