Re: [scala] Unsoundness in overriding methods with higher-order type parameters?

> Hi Vladimir,
> You're right. That's a bug :-(
> Working on a fix now -- could you please file a ticket?
>
> cheers
> adriaan
>
> On Tue, Jun 16, 2009 at 4:04 PM, Vladimir Reshetnikov <
> v.reshetnikov@...> wrote:
>
>> I use Scala 2.7.5 final.
>>
>> Vladimir
>>
>> On 6/16/09, James Iry <jamesiry@...> wrote:
>> > Oops, missed the cast to an A.  Indeed that's a problem
>> >
>> > trait A {
>> >   def f[T[_]](x : T[Int]) : T[Any]
>> > }
>> >
>> > class B extends A {
>> >   def f[T[+_]](x : T[Int]) : T[Any] = x
>> > }
>> >
>> > class P[Y](var y : Y)
>> >
>> >
>> > val p = new P(1)
>> >
>> > val palias = (new B():A).f[P](p)
>> >
>> > palias.y = "hello"
>> >
>> > scala> p.y
>> > java.lang.ClassCastException: java.lang.String cannot be cast to
>> > java.lang.Integer
>> >
>> >
>> >
>> > On Tue, Jun 16, 2009 at 6:51 AM, James Iry <jamesiry@...> wrote:
>> >
>> >> Which version of Scala are you running?  In both 2.7.5 and
>> >> 2.8.0.something
>> >> I get
>> >>
>> >> <console>:7: error: kinds of the type arguments (P) do not conform to
>> the
>> >> expected kinds of the type parameters (type T).
>> >> P's type parameters do not match type T's expected parameters: type Y
>> >> is
>> >> invariant, but type _ is declared covariant
>> >>        val palias = new B().f[P](new P[Int](1))
>> >>
>> >>
>> >> On Tue, Jun 16, 2009 at 6:27 AM, Vladimir Reshetnikov <
>> >> v.reshetnikov@...> wrote:
>> >>
>> >>> Hi,
>> >>>
>> >>> Consider the following code:
>> >>>
>> >>> //////////////////////////////////////////////////
>> >>> trait A {
>> >>>  def f[T[_]](x : T[Int]) : T[Any]
>> >>> }
>> >>>
>> >>> class B extends A {
>> >>>  def f[T[+_]](x : T[Int]) : T[Any] = x
>> >>> }
>> >>>
>> >>> class P[Y](var y : Y)
>> >>> //////////////////////////////////////////////////
>> >>>
>> >>> It accepted by the Scala 2.7.5 compiler without any errors. But is
>> >>> seems unsound, because then we can write (new B:A).f[P](new
>> >>> P[Int](1)), and nonvariant P[Int] is coerced to P[Any].
>> >>>
>> >>> Thanks,
>> >>> Vladimir
>> >>>
>> >>
>> >>
>> >
>>
>>
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>