Problem with traits

[Albert Strasheim]

Hello all

I'm having a problem with traits that I would appreciate some help with:

I have the following two classes, each with a ! method:

class Foo {
  def !(message: Any) = println("foo: " + message)
}

class Baz {
  def !(message: Any) = println("baz: " + message)
}

First, a trait with a self-type only for Foo:

trait Bar {
  self: Foo =>
    def bang(message: Any) = {
      self ! message
    }
}

This compiles without problems and works fine. But if I do:

trait Bar2 {
  self =>
    def bang(message: Any) = {
      self ! message
    }
}

I get the following compiler error:

error: value ! is not a member of Bar2

The rest of the code:

object TraitStuff {
  def main(args : Array[String]) {
    val foo = new Foo with Bar
    val baz = new Baz with Bar2
    foo.bang("bar")
    baz.bang("bar")
  }
}

I'm using scala-2.8.0.r19180-b20091021023451. Any help would be appreciated.

Regards,

Albert

[Detering Dirk-2]

> I'm having a problem with traits that I would appreciate some
> help with:
>
> I have the following two classes, each with a ! method:
>
> class Foo {
>   def !(message: Any) = println("foo: " + message) }
>
> class Baz {
>   def !(message: Any) = println("baz: " + message) }
>
> First, a trait with a self-type only for Foo:
>
> trait Bar {
>   self: Foo =>
>     def bang(message: Any) = {
>       self ! message
>     }
> }
>
> This compiles without problems and works fine. But if I do:
>
> trait Bar2 {
>   self =>

Is it intentionally that you left out the
specific type here?
(You declared it in Bar with self: Foo =>,
but not here in Bar2)

>     def bang(message: Any) = {
>       self ! message
>     }
> }
>
> I get the following compiler error:
>
> error: value ! is not a member of Bar2
>
> The rest of the code:
>
> object TraitStuff {
>   def main(args : Array[String]) {
>     val foo = new Foo with Bar
>     val baz = new Baz with Bar2
>     foo.bang("bar")
>     baz.bang("bar")
>   }
> }
>
> I'm using scala-2.8.0.r19180-b20091021023451. Any help would
> be appreciated.
>
> Regards,
>
> Albert
> --
> View this message in context:
> http://old.nabble.com/Problem-with-traits-tp26157101p26157101.html
> Sent from the Scala - User mailing list archive at Nabble.com.
>
>

[Albert Strasheim]

Hello all

On Mon, Nov 2, 2009 at 5:33 PM, Detering Dirk <Dirk.Detering@...> wrote:

>> trait Bar {
>>   self: Foo =>
>>     def bang(message: Any) = {
>>       self ! message
>>     }
>> }
>> This compiles without problems and works fine. But if I do:
>>
>> trait Bar2 {
>>   self =>
> Is it intentionally that you left out the
> specific type here?
> (You declared it in Bar with self: Foo =>,
> but not here in Bar2)
>>     def bang(message: Any) = {
>>       self ! message
>>     }
>> }
>> I get the following compiler error:
>> error: value ! is not a member of Bar2

Yes, it's intentional. I am trying to make a trait that works for any
class that has a ! method.

Regards,

Albert

[David Hall-17]

On Mon, Nov 2, 2009 at 10:28 PM, Albert Strasheim <fullung@...> wrote:

> Hello all
>
> On Mon, Nov 2, 2009 at 5:33 PM, Detering Dirk <Dirk.Detering@...> wrote:
>>> trait Bar {
>>>   self: Foo =>
>>>     def bang(message: Any) = {
>>>       self ! message
>>>     }
>>> }
>>> This compiles without problems and works fine. But if I do:
>>>
>>> trait Bar2 {
>>>   self =>
>> Is it intentionally that you left out the
>> specific type here?
>> (You declared it in Bar with self: Foo =>,
>> but not here in Bar2)
>>>     def bang(message: Any) = {
>>>       self ! message
>>>     }
>>> }
>>> I get the following compiler error:
>>> error: value ! is not a member of Bar2
>
> Yes, it's intentional. I am trying to make a trait that works for any
> class that has a ! method.

But Bar2 doesn't list any requirement that its selftype requires def !...

Why can't you just say:

scala> trait Bar2 {
     | def !(m: Any): Unit;
     | def bang(m: Any) = { this ! m }
     | }
defined trait Bar2

scala> class Foo { def !(m: Any) {} }
defined class Foo

scala> new Foo with Bar2;
res3: Foo with Bar2 = $anon$1@23f39712

or, more ridiculously:

scala> type BangHaver = { def !(m: Any): Unit }
defined type alias BangHaver

scala> trait Bar2 { self: BangHaver => def bang(m: Any) = { self ! m } }
defined trait Bar2

scala> class Foo { def !(m: Any) {} }
defined class Foo

scala> new Foo with Bar2;
res0: Foo with Bar2 = $anon$1@44b1d2a0

-- David

>
> Regards,
>
> Albert
>

[Albert Strasheim]

Hello all

On Tue, Nov 3, 2009 at 8:37 AM, David Hall <dlwh@...> wrote:
> But Bar2 doesn't list any requirement that its selftype requires def !...

Thanks, I've figured that part out now.

On to the more complex problem I am actually trying to solve:

import scala.actors.Actor._

case class Ping(other: GenericPinger)

object Actors {
  def main(args : Array[String]) {
    val p1 = new AkkaPinger()
    p1.start
    val p2 = new ScalaPinger()
    p2.start
    p1 ! Ping(p2)
  }
}

trait GenericPinger {
  // XXX would like to get rid of this method in the trait
  def bang(message: AnyRef): Unit

  def reallyReceive: PartialFunction[Any, Unit] = {
    case Ping(other) => {
      println(this + " Ping!")
      other.bang(Ping(this)) // XXX would like to write this as: other
! Ping(this)
    }
  }
}

class AkkaPinger extends se.scalablesolutions.akka.actor.Actor with
GenericPinger {
  def receive: PartialFunction[Any, Unit] = reallyReceive
  // XXX would like to get rid of this extra method
  def bang(message: AnyRef): Unit = {this.!(message)}
}

class ScalaPinger extends scala.actors.Actor with GenericPinger {
  def act() = {
    loop {
      react(reallyReceive)
    }
  }
  // XXX would like to get rid of this extra method
  def bang(message: AnyRef): Unit = {this.!(message)}
}

As far as I understand, the problem I'm having now is that the
signatures for the Scala Actors ! method and the Akka Actors ! method
look slightly different, and I have no idea how to craft a self-type
declaration to make the trait see the respective ! methods.

The Scala Actors ! definition lives here (more or less...):

https://lampsvn.epfl.ch/trac/scala/browser/scala/trunk/src/actors/scala/actors/AbstractReactor.scala

And the Akka Actors one live here:

http://akka.scalablesolutions.se/scaladoc/akka-actors/se/scalablesolutions/akka/actor/Actor.html

Thanks for any thoughts.

Regards,

Albert

P.S. We'll probably settle on using Akka Actors for our library in the
end, but right now I'm trying to code up a little benchmark suite
comparing the two actor libraries, because we are having some
performance issues. So my goal is to minimize the amount of duplicated
code between my actor implementations.

[David Hall-17]

On Tue, Nov 3, 2009 at 12:32 AM, Albert Strasheim <fullung@...> wrote:

> Hello all
>
> On Tue, Nov 3, 2009 at 8:37 AM, David Hall <dlwh@...> wrote:
>> But Bar2 doesn't list any requirement that its selftype requires def !...
>
> Thanks, I've figured that part out now.
>
> On to the more complex problem I am actually trying to solve:
>
> import scala.actors.Actor._
>
> case class Ping(other: GenericPinger)
>
> object Actors {
>  def main(args : Array[String]) {
>    val p1 = new AkkaPinger()
>    p1.start
>    val p2 = new ScalaPinger()
>    p2.start
>    p1 ! Ping(p2)

>  }
> }
>
> trait GenericPinger {
>  // XXX would like to get rid of this method in the trait
>  def bang(message: AnyRef): Unit
>
>  def reallyReceive: PartialFunction[Any, Unit] = {
>    case Ping(other) => {
>      println(this + " Ping!")
>      other.bang(Ping(this)) // XXX would like to write this as: other
> ! Ping(this)
>    }
>  }
> }

maybe something like:

trait GenericParser[-Msg] {
  def !(message: Msg):Unit;
   // ...
}

and then

 class AkkaPinger extends se.scalablesolutions.akka.actor.Actor with
GenericPinger[Object];
class ScalaPinger extends scala.actors.Actor with GenericPinger[Any];

?
-- David

>
> class AkkaPinger extends se.scalablesolutions.akka.actor.Actor with
> GenericPinger {
>  def receive: PartialFunction[Any, Unit] = reallyReceive
>  // XXX would like to get rid of this extra method
>  def bang(message: AnyRef): Unit = {this.!(message)}
> }
>
> class ScalaPinger extends scala.actors.Actor with GenericPinger {
>  def act() = {
>    loop {
>      react(reallyReceive)
>    }
>  }
>  // XXX would like to get rid of this extra method
>  def bang(message: AnyRef): Unit = {this.!(message)}
> }
>
> As far as I understand, the problem I'm having now is that the
> signatures for the Scala Actors ! method and the Akka Actors ! method
> look slightly different, and I have no idea how to craft a self-type
> declaration to make the trait see the respective ! methods.
>
> The Scala Actors ! definition lives here (more or less...):
>
> https://lampsvn.epfl.ch/trac/scala/browser/scala/trunk/src/actors/scala/actors/AbstractReactor.scala
>
> And the Akka Actors one live here:
>
> http://akka.scalablesolutions.se/scaladoc/akka-actors/se/scalablesolutions/akka/actor/Actor.html
>
> Thanks for any thoughts.
>
> Regards,
>
> Albert
>
> P.S. We'll probably settle on using Akka Actors for our library in the
> end, but right now I'm trying to code up a little benchmark suite
> comparing the two actor libraries, because we are having some
> performance issues. So my goal is to minimize the amount of duplicated
> code between my actor implementations.