RFR: 8343580: Type error with inner classes of generic classes in functions generic by outer
Vicente Romero
vromero at openjdk.org
Wed May 21 18:08:51 UTC 2025
On Wed, 21 May 2025 09:55:31 GMT, Aggelos Biboudis <abimpoudis at openjdk.org> wrote:
> javac determines erroneously that `getter` has a raw type (`G.Getter`). The type of `getter` is deduced as the raw type `Getters<T>.Getter` by javac. Thus, the `Object` in the following example. The question is whether it should be treated as raw or not in the scenario where the qualifying type *is* a type parameter, as in `G.Getter`. In this case `Getter` is inherited from the supertype `Getters<T>`:
>
>
> static abstract class Getters<T> {
> abstract class Getter {
> abstract T get();
> }
> }
>
> static class Usage<T, G extends Getters<T>> {
> public T test(G.Getter getter) {
> return getter.get(); // incompatible types: Object cannot be converted to T
> }
> }
>
>
> It seems that this is a compiler bug. According to 4.8 Raw Types a “rare” type occurs when the inner is a partially raw type but the definition of Getter doesn’t take any type variables, so this is not a case of a "rare" type. `G.Getter` describes a type with a qualifying type being a type parameter which is not raw and moreover there is an instantiation of its bound. Simply not looking into the bounds of `G` seems like a compiler bug.
isn't this test case similar and we get the same error message:
abstract class Getters<T> {
abstract class Getter {
abstract T get();
}
}
class G2<K> extends Getters<K> {}
class Usage<M, L> {
M test(G2<L>.Getter getter) {
return getter.get();
}
}
-------------
PR Comment: https://git.openjdk.org/jdk/pull/25346#issuecomment-2898805446
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