2.0-RC1: foo is not assignable from class bar

[G J]

A simple akka test programs in 2.0-RC1 now generate an error:
interface foobar is not assignable from class foobaz.

This did not occur in earlier versions, and appears to be restricted
to the interactive loop. The test program runs fine under sbt.

What gives? What do I need to do to continue running in the REPL?

Appreciated.

[√iktor Ҡlang]

Akka uses the context classloader of the thread that creates the actor system. Try to set it to null before.

Cheers,
V

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[Jonas Bonér]

Could you post the simple program? It could assist us understanding the question.

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On Feb 14, 2012 9:42 PM, "G J" <oda...@gmail.com> wrote:

[G J]

A trivial test program is pasted below.

In sbt, execute compile and then run. Under the REPL if you import and
try and run Test.jolly, you should get the error:

java.lang.ClassCastException: interface akka.actor.ActorRefProvider is
not assignable from class akka.actor.LocalActorRefProvider

Thanks.

[Plz. Not class hakkery again...]
---------------------------------------------------
package test.akka

import akka.actor
import akka.util.duration._

object Test extends App {
class Jolly extends actor.Actor {
def receive = {
case "start" =>
context.setReceiveTimeout(5 * 1000 milliseconds)
case actor.ReceiveTimeout =>
println("Jolly good> timeout")
}
}

def jolly {
val system = actor.ActorSystem("Jolly")
val toll = system.actorOf(actor.Props[Jolly], name = "jolly")
toll ! "start"
}

override def main(args: Array[String]) = jolly

[Peter Vlugter]

I had no problems with running this in a test project. Here's the output I see:

sbt> run
[info] Running test.akka.Test
Jolly good> timeout
Jolly good> timeout
Jolly good> timeout
…

sbt> console
[info] Starting scala interpreter...
[info]
Welcome to Scala version 2.9.1.final (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_29).
Type in expressions to have them evaluated.
Type :help for more information.

scala> import test.akka.Test
import test.akka.Test

scala> Test.jolly

scala> Jolly good> timeout
Jolly good> timeout
Jolly good> timeout
...

[G J]

Interesting indeed.

It runs fine for me too when I run it under the console through sbt
the way you describe. However, if I run it using:

scala -classpath <path to classes and jar>

and import and execute, I do get the error I mentioned.

Why does running scala directly yield the error...?

Thanks.

[Peter Vlugter]

On 15/02/2012, at 4:49 PM, G J wrote:

> Interesting indeed.
>
> It runs fine for me too when I run it under the console through sbt
> the way you describe. However, if I run it using:
>
> scala -classpath <path to classes and jar>
>
> and import and execute, I do get the error I mentioned.
>
> Why does running scala directly yield the error...?

Each line in the repl runs in a separate thread. If you add the -Yrepl-sync option it should work fine.

You could also set the context classloader with something like:

{ Thread.currentThread.setContextClassLoader(Test.getClass.getClassLoader); Test.jolly }

[Mike Slinn]

Where is -Yrepl-sync documented?

Mike

[Peter Vlugter]

On 15/02/2012, at 7:19 PM, Mike Slinn wrote:

> Where is -Yrepl-sync documented?

I don't know if there's richer documentation but scala -Y lists all the -Y options with short descriptions.

[G J]

Yes. Both those suggestions made it work, yet I fail to understand
what the class loader has to do with it. For that matter, I would
never have guessed to look at repl-sync either.

Would highly appreciated a brief explanation.

Thanks.

[√iktor Ҡlang]

Akka uses the context class loader from the thread that created the ActorSystem, and since every line is on it's own loader, you¨ll have ap roblem if you don¨t use that.

We should document it. Open a ticket.

Thanks!

Cheers,

√

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Viktor Klang

Akka Tech Lead

Typesafe - The software stack for applications that scale

Twitter: @viktorklang