Strange type matching

This is type erasure again...In the JVM, AnyVal == AnyRef == Object


On Fri, Sep 11, 2009 at 10:46 AM, Olaf Burkart <olaf [dot] burkart [at] itemis [dot] de> wrote:

Hi,
I just came across the following type match problem:

object MatchTest {

 def dispatch(any: Any) =
  any match {
    case anyRef: AnyRef => "AnyRef"
    case anyVal: AnyVal => "AnyVal"
  }
  def main(args : Array[String]) : Unit = {
  println("Boolean: " + dispatch(true))
  println("Integer: " + dispatch(1))
  println("List: " + dispatch(List()))
 }
}

with the output

Boolean: AnyRef
Integer: AnyRef
List: AnyRef

Am I correct in assuming that this is compiler bug, as I would expect a Boolean, as well as an Integer, to be a subtype of AnyVal?

Cheers, Olaf Burkart

Not type erasure, actually. Type erasure is something that happens to parameterized types. This is a consequence of JVM not handling Java primitive types as classes, which clashes with Scala's conception of everything being an object.

On Fri, Sep 11, 2009 at 7:16 AM, Kevin Wright <kev [dot] lee [dot] wright [at] googlemail [dot] com> wrote:

This is type erasure again... In the JVM, AnyVal == AnyRef == Object


On Fri, Sep 11, 2009 at 10:46 AM, Olaf Burkart <olaf [dot] burkart [at] itemis [dot] de> wrote:

Hi,
I just came across the following type match problem:

object MatchTest {

 def dispatch(any: Any) =
  any match {
    case anyRef: AnyRef => "AnyRef"
    case anyVal: AnyVal => "AnyVal"
  }
  def main(args : Array[String]) : Unit = {
  println("Boolean: " + dispatch(true))
  println("Integer: " + dispatch(1))
  println("List: " + dispatch(List()))
 }
}

with the output

Boolean: AnyRef
Integer: AnyRef
List: AnyRef

Am I correct in assuming that this is compiler bug, as I would expect a Boolean, as well as an Integer, to be a subtype of AnyVal?

Cheers, Olaf Burkart

--
Daniel C. Sobral

Something I learned in academia: there are three kinds of academic reviews: review by name, review by reference and review by value.

Guess I never thought of it that way...
I just have this little mental box labeled "lack of reification" which I use to hold this sort of problem, along with a suitable choice of expletives :)

On Fri, Sep 11, 2009 at 2:46 PM, Daniel Sobral <dcsobral [at] gmail [dot] com> wrote:

Not type erasure, actually. Type erasure is something that happens to parameterized types. This is a consequence of JVM not handling Java primitive types as classes, which clashes with Scala's conception of everything being an object.

On Fri, Sep 11, 2009 at 7:16 AM, Kevin Wright <kev [dot] lee [dot] wright [at] googlemail [dot] com> wrote:

This is type erasure again... In the JVM, AnyVal == AnyRef == Object


On Fri, Sep 11, 2009 at 10:46 AM, Olaf Burkart <olaf [dot] burkart [at] itemis [dot] de> wrote:

Hi,
I just came across the following type match problem:

object MatchTest {

 def dispatch(any: Any) =
  any match {
    case anyRef: AnyRef => "AnyRef"
    case anyVal: AnyVal => "AnyVal"
  }
  def main(args : Array[String]) : Unit = {
  println("Boolean: " + dispatch(true))
  println("Integer: " + dispatch(1))
  println("List: " + dispatch(List()))
 }
}

with the output

Boolean: AnyRef
Integer: AnyRef
List: AnyRef

Am I correct in assuming that this is compiler bug, as I would expect a Boolean, as well as an Integer, to be a subtype of AnyVal?

Cheers, Olaf Burkart

--
Daniel C. Sobral

Something I learned in academia: there are three kinds of academic reviews: review by name, review by reference and review by value.

Yeah, scala trying to rectify primitives with objects is very handy inside scala, but can cause strange issues when interfacing Java + Scala.

e.g. we use Scala 2.7.4 in production at work.  I find myself sometimes having to explicitly declare overridden methods with java.lang.Long instead of just Long.   I also find that when using java collections, you always have to explicitly state java's "big" Long instead of scala's Long.  It's a minor annoyance, as sometimes this also kills the Rich* implicits.


That's why:

Pro Scala Tip #XYZ-   When mixing Scala and Java, prefer primitives in your Java interfaces.


- Josh


On Fri, Sep 11, 2009 at 10:23 AM, Kevin Wright <kev [dot] lee [dot] wright [at] googlemail [dot] com> wrote:

Guess I never thought of it that way...
I just have this little mental box labeled "lack of reification" which I use to hold this sort of problem, along with a suitable choice of expletives :)

On Fri, Sep 11, 2009 at 2:46 PM, Daniel Sobral <dcsobral [at] gmail [dot] com> wrote:

Not type erasure, actually. Type erasure is something that happens to parameterized types. This is a consequence of JVM not handling Java primitive types as classes, which clashes with Scala's conception of everything being an object.

On Fri, Sep 11, 2009 at 7:16 AM, Kevin Wright <kev [dot] lee [dot] wright [at] googlemail [dot] com> wrote:

This is type erasure again... In the JVM, AnyVal == AnyRef == Object


On Fri, Sep 11, 2009 at 10:46 AM, Olaf Burkart <olaf [dot] burkart [at] itemis [dot] de> wrote:

Hi,
I just came across the following type match problem:

object MatchTest {

 def dispatch(any: Any) =
  any match {
    case anyRef: AnyRef => "AnyRef"
    case anyVal: AnyVal => "AnyVal"
  }
  def main(args : Array[String]) : Unit = {
  println("Boolean: " + dispatch(true))
  println("Integer: " + dispatch(1))
  println("List: " + dispatch(List()))
 }
}

with the output

Boolean: AnyRef
Integer: AnyRef
List: AnyRef

Am I correct in assuming that this is compiler bug, as I would expect a Boolean, as well as an Integer, to be a subtype of AnyVal?

Cheers, Olaf Burkart

--
Daniel C. Sobral

Something I learned in academia: there are three kinds of academic reviews: review by name, review by reference and review by value.