Re: [scala] Structural types within classes with contravariant type parameters are unsound

> Do you imply variance can and should be checked right away? That would be
> just great (but may cause a lot of frustration among developers unless
> there's a proper error message).
>
> 2009/6/18 Vladimir Reshetnikov <v.reshetnikov@...>
>
>> Hi,
>>
>> Consider the following code:
>> ////////////////////////////////////////
>> class A[-S](y : S) {
>>  val f  = new { val x = y }
>> }
>> ////////////////////////////////////////
>>
>> It compiles without any errors. But now we can write:
>>
>> scala> val a = new A(1)
>> a: A[Int] = A@43e3ac
>>
>> scala> val b = a : A[Nothing]
>> b: A[Nothing] = A@43e3ac
>>
>> scala> b.f.x
>> java.lang.ClassCastException: java.lang.Integer cannot be cast to
>> scala.runtime.Nothing$
>>        at .<init>(<console>:8)
>>        at .<clinit>(<console>)
>>        at RequestResult$.<init>(<console>:4)
>>        at RequestResult$.<clinit>(<console>)
>>        at RequestResult$result(<console>)
>>        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
>>        at
>> sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorIm...
>>
>> Looks like unsoundness.
>>
>> Thanks,
>> Vladimir
>>
>
>
>
> --
> Thanks,
> -Vlad
>