Type-variable references from local interface declaration
Tagir Valeev
amaembo at gmail.com
Mon Jun 15 12:04:39 UTC 2020
Same with records. For some reason I thought I checked this before,
but this code is compilable both in 14-preview and 15-preview, which
looks incorrect:
class LocalRecord {
static <U> void test() {
record R() {
U get() {return null;}
}
}
}
With best regards,
Tagir Valeev.
On Mon, Jun 15, 2020 at 6:45 PM Tagir Valeev <amaembo at gmail.com> wrote:
>
> Hello!
>
> The same problem appears for local enums as well. And, I believe, it
> causes type system unsoundness:
>
> class LocalEnum {
> static <U> U getAndSet(U u) {
> enum X {
> A;
> U u;
> }
> U old = X.A.u;
> X.A.u = u;
> return old;
> }
>
> public static void main(String[] args) {
> String s = getAndSet("foo");
> Integer i = getAndSet(123);
> }
> }
>
> This code can be compiled without error or warning, yet it produces
> ClassCastException when executed.
>
> With best regards,
> Tagir Valeev.
>
> On Mon, Jun 15, 2020 at 6:38 PM Tagir Valeev <amaembo at gmail.com> wrote:
> >
> > Hello!
> >
> > The spec draft for local interfaces and enums [1] tells that it's
> > illegal to refer to the enclosing method type parameter from the local
> > interface. Here's a simplified sample from the spec:
> >
> > class Box<T> {
> > static <U> Box<U> make(U val) {
> > interface Checker {
> > void check(U val); // compile-time error
> > }
> > return null;
> > }
> > }
> >
> > However, it's successfully compilable using javac 15-ea+26-1287. I
> > believe, either spec or implementation should be adjusted.
> >
> > With best regards,
> > Tagir Valeev.
> >
> > [1] http://cr.openjdk.java.net/~gbierman/jep384/jep384-20200506/specs/local-statics-jls.html#jls-6.5.5.1
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