I have a problem that can be summarised by the following Java classes:
public class Foo<T extends Foo> {}
public class Bar<T extends Foo> {}
public interface AnInterface {
public <T extends Foo, S extends Bar<T>> void doSomething(T thing, S other);
}
I am trying to implement AnInterface
from Scala code and this is what my IDE advices:
class AnImplementation extends AnInterface {
override def doSomething[T <: Foo[_], S <: Bar[T]](thing: T, other: S): Unit = ???
}
This doesn't compile as the compiler produces the following error:
type arguments [T] do not conform to class Bar's type parameter bounds [T <: foo.Foo[_ <: foo.Foo[_ <: foo.Foo[_ <: AnyRef]]]]
I tried to fix this in several ways; some failed experiments are:
// Failing with: method doSomething has incompatible type
override def doSomething[T <: Foo[_ <: Foo[_]], S <: Bar[T]](thing: T, other: S): Unit = ???
// Failing with: illegal cyclic reference involving type T
override def doSomething[T <: Foo[_ <: T], S <: Bar[T]](thing: T, other: S): Unit = ???
// Failing with: illegal cyclic reference involving type T
override def doSomething[T <: Foo[V] forSome { type V <: T }, S <: Bar[T]](thing: T, other: S): Unit = ???
// Failing with: method doSomething has incompatible type
override def doSomething[T <: Foo[V] forSome { type V <: Foo[_] }, S <: Bar[T]](thing: T, other: S): Unit = ???
Does anyone have an idea about how to get around this issue? Is it not possible to implement such a Java interface from Scala?
It looks like you're not parameterizing the classes correctly. I believe this is what you're after:
public class Foo<T extends Foo<T>> {}
public class Bar<T extends Foo<T>> {}
public interface AnInterface {
<T extends Foo<T>, S extends Bar<T>> void doSomething(T thing, S other);
}
Then the implementation becomes:
class AnImplementation extends AnInterface {
override def doSomething[T <: Foo[T], S <: Bar[T]](thing:T, other:S):Unit = ???
}
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