gmane.comp.lang.scala

illegal match allowed by scalac

Hi,
the following session fails with MatchError for obvious reasons, but the compiler is happy with this code. Should it signal it? (I'm using 2.7.2-RC2)

scala> class ScType
defined class ScType

scala> var t : Option[ScType] = Some(new ScType)
t: Option[ScType] = Some(ScType <at> 17ccb2f)

scala> class ScalaResolveResult
defined class ScalaResolveResult

scala> t match {case Some(r : ScalaResolveResult) => r case None => null}
scala.MatchError: Some(ScType <at> 17ccb2f)
        at .<init>(<console>:8)
        at .<clinit>(<console>)
        at RequestResult$.<init>(<console>:3)
        at RequestResult$.<clinit>(<console>)
        at RequestResult$result(<console>)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unkn...
scala>

Eugene.

headers

martin odersky | 13 Oct 18:49

Re: illegal match allowed by scalac

I think at the moment exhaustiveness checking is done only for
constructor patterns, not for type patterns like the one your wrote.

Cheers

 -- Martin

On Mon, Oct 13, 2008 at 6:44 PM, Eugene Vigdorchik
<eugene.vigdorchik <at> gmail.com> wrote:
> Hi,
> the following session fails with MatchError for obvious reasons, but the
> compiler is happy with this code. Should it signal it? (I'm using 2.7.2-RC2)
>
> scala> class ScType
> defined class ScType
>
> scala> var t : Option[ScType] = Some(new ScType)
> t: Option[ScType] = Some(ScType <at> 17ccb2f)
>
> scala> class ScalaResolveResult
> defined class ScalaResolveResult
>
> scala> t match {case Some(r : ScalaResolveResult) => r case None => null}
> scala.MatchError: Some(ScType <at> 17ccb2f)
>         at .<init>(<console>:8)
>         at .<clinit>(<console>)
>         at RequestResult$.<init>(<console>:3)
>         at RequestResult$.<clinit>(<console>)
>         at RequestResult$result(<console>)
>         at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
>         at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
>         at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unkn...
> scala>
>
> Eugene.
>

headers

Eugene Vigdorchik | 13 Oct 19:07

Re: illegal match allowed by scalac

I think it is not about exhaustiveness, but rather typed pattern not conforming to expected type. Does scala allow this?

On Mon, Oct 13, 2008 at 8:49 PM, martin odersky <martin.odersky <at> epfl.ch> wrote:

I think at the moment exhaustiveness checking is done only for
constructor patterns, not for type patterns like the one your wrote.

Cheers

-- Martin

On Mon, Oct 13, 2008 at 6:44 PM, Eugene Vigdorchik
<eugene.vigdorchik <at> gmail.com> wrote:
> Hi,
> the following session fails with MatchError for obvious reasons, but the
> compiler is happy with this code. Should it signal it? (I'm using 2.7.2-RC2)
>
> scala> class ScType
> defined class ScType
>
> scala> var t : Option[ScType] = Some(new ScType)
> t: Option[ScType] = Some(ScType <at> 17ccb2f)
>
> scala> class ScalaResolveResult
> defined class ScalaResolveResult
>
> scala> t match {case Some(r : ScalaResolveResult) => r case None => null}
> scala.MatchError: Some(ScType <at> 17ccb2f)
> at .<init>(<console>:8)
> at .<clinit>(<console>)
> at RequestResult$.<init>(<console>:3)
> at RequestResult$.<clinit>(<console>)
> at RequestResult$result(<console>)
> at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
> at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unkn...
> scala>
>
> Eugene.
>

headers

Geoffrey Alan Washburn | 13 Oct 19:10

Re: illegal match allowed by scalac

Eugene Vigdorchik wrote:
> I think it is not about exhaustiveness, but rather typed pattern not 
> conforming to expected type. 

Right.  I would have thought the same code that handles GADT refinements 
would have indicated that the case could not possibly typecheck.