pattern matching with type parameters

[PetarM]

Hi all,

Is it possible to pattern match case classes with type parameters. E.g. if I have

  case class Msg[T]()

Can I have a match like this:

  receive {
    case Msg[T] => ... some code that uses the type information T ...
  }

I know that the code above does not compile, but is there a way to mimic its meaning?

Thanks,
Petar

[David Hall-15]

scala> case class Msg[T](implicit val manifest: scala.reflect.Manifest[T])
defined class Msg

scala> case class StrMsg(s: String) extends Msg[String];
defined class StrMsg

scala> (StrMsg("3"):Msg[String]) match { case m@ Msg() => println(m.manifest) }
java.lang.String

Not perfect, but it's a start.

-- David

On Thu, May 28, 2009 at 4:24 PM, PetarM <petarm@...> wrote:

>
> Hi all,
>
> Is it possible to pattern match case classes with type parameters. E.g. if I
> have
>
>  case class Msg[T]()
>
> Can I have a match like this:
>
>  receive {
>    case Msg[T] => ... some code that uses the type information T ...
>  }
>
> I know that the code above does not compile, but is there a way to mimic its
> meaning?
>
> Thanks,
> Petar
>
>
> --
> View this message in context: http://www.nabble.com/pattern-matching-with-type-parameters-tp23771884p23771884.html
> Sent from the Scala mailing list archive at Nabble.com.
>
>

[Alex Boisvert-3]

(Moving to -debate since I'm asking controversial question...)

It seems manifest are quite important for

Why not have one scala.reflect.Manifest automatically added to all Scala classes for each type parameter and type member?

Would this be such a memory or performance burden?   And if it is, maybe we could have an annotation to disable the feature.

On Thu, May 28, 2009 at 4:29 PM, David Hall <dlwh@...> wrote:

scala> case class Msg[T](implicit val manifest: scala.reflect.Manifest[T])
defined class Msg

scala> case class StrMsg(s: String) extends Msg[String];
defined class StrMsg

scala> (StrMsg("3"):Msg[String]) match { case m@ Msg() => println(m.manifest) }
java.lang.String

Not perfect, but it's a start.

-- David

On Thu, May 28, 2009 at 4:24 PM, PetarM <petarm@...> wrote:
>
> Hi all,
>
> Is it possible to pattern match case classes with type parameters. E.g. if I
> have
>
>  case class Msg[T]()
>
> Can I have a match like this:
>
>  receive {
>    case Msg[T] => ... some code that uses the type information T ...
>  }
>
> I know that the code above does not compile, but is there a way to mimic its
> meaning?
>
> Thanks,
> Petar
>
>
> --
> View this message in context: http://www.nabble.com/pattern-matching-with-type-parameters-tp23771884p23771884.html
> Sent from the Scala mailing list archive at Nabble.com.
>
>

[Alex Boisvert-3]

(Damn these send buttons that triggers by themselves!!  Here's what I was writing...)

It seems manifests are quite important and generally useful to support good OO practices.

Why not have one scala.reflect.Manifest automatically added to all Scala classes for each type parameter and type member?

Would this be such a memory or performance burden?   And if it is, maybe we could have an annotation to disable the feature? 

I'm feeling we're going down the boilerplate road with this... maybe when manifests are fully fleshed out and no longer experimental they could be tightly integrated in the language?

alex

On Thu, May 28, 2009 at 4:37 PM, Alex Boisvert <boisvert@...> wrote:

(Moving to -debate since I'm asking controversial question...)

It seems manifest are quite important for

Why not have one scala.reflect.Manifest automatically added to all Scala classes for each type parameter and type member?

Would this be such a memory or performance burden?   And if it is, maybe we could have an annotation to disable the feature.

On Thu, May 28, 2009 at 4:29 PM, David Hall <dlwh@...> wrote:

scala> case class Msg[T](implicit val manifest: scala.reflect.Manifest[T])
defined class Msg

scala> case class StrMsg(s: String) extends Msg[String];
defined class StrMsg

scala> (StrMsg("3"):Msg[String]) match { case m@ Msg() => println(m.manifest) }
java.lang.String

Not perfect, but it's a start.

-- David

On Thu, May 28, 2009 at 4:24 PM, PetarM <petarm@...> wrote:
>
> Hi all,
>
> Is it possible to pattern match case classes with type parameters. E.g. if I
> have
>
>  case class Msg[T]()
>
> Can I have a match like this:
>
>  receive {
>    case Msg[T] => ... some code that uses the type information T ...
>  }
>
> I know that the code above does not compile, but is there a way to mimic its
> meaning?
>
> Thanks,
> Petar
>
>
> --
> View this message in context: http://www.nabble.com/pattern-matching-with-type-parameters-tp23771884p23771884.html
> Sent from the Scala mailing list archive at Nabble.com.
>
>