Allowing a type parameter to extend more than one type.

[FabrizioG202]

I have the following classes while building a package to abstract reading of different sources:

• ReadMixin on DataSource, which provides a read() method.
• SeekMixin on DataSource, which provides a seek(position) method.

Some DataSources, for example one wrapping a file implement both.

Is there currently a way to define a function which accepts a DataSource which implements Both mixins? I would expect somethhing like this to work:

T myFunction<T extends ReadMixin with SeekMixin>(T param) {}

but it does not.

I have found similar issues asking for a similar concepts but for unrelated types, like #2161 (String and Iterable<String>), but I have not found an issue talking about 'related' types, like what I am trying to achieve.

Is there currently a way to do this?

[lrhn]

There is no way to do that in the current langauge. Each mixin introduces a new type, and those types are unrelated.
They happen to have a shared supertype, but all types do (if nothing else then Object?).

There are other requests for multiple upper bounds, fx #2709 and #1152.
I'll defer to those issues.