RFR: [type-classes] Initial work to enable type-classes mediated operator support [v2]

[Joe Darcy]

On Mon, 26 Jan 2026 17:29:47 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

> > @mcimadamore , what are the conditions to allow to a class to participate in having a witness, is being a value class sufficient?
> > I was working on update Bfloat16 to have a witness for StandardFloatingPoint, but the client code wasn't recognizing the operators as valid for Bfloat16 arguments. Perhaps recognizing as allowing both Numerical and Orderable operators isn't work yet.
> > After switching to a Numerical witness in a Bfloat16 value class, the code was accepted by the compiler, but ran into VerifyErrors at runtime. I'll send you more information off-list. Thanks.
> 
> I've addressed the verifier issues here:
> 
> https://git.openjdk.org/valhalla/pull/1968
> 
> As for the other issue you mentioned -- note that if you want to apply an operation that belongs to the Numerical class, such as `+`, you need to have a witness for Numerical. In other words, Bfloat16 needs to have witnesses for both Numerical, StandardFloating point and Orderable.
> 
> At the moment "type class extension" is a bit clunky, so the various witnesses have to be provided and wired manually, as shown in this test:
> 
> https://github.com/mcimadamore/valhalla/blob/2b56b03d734a2f82f9ef978d11811245ddc30a1d/test/langtools/tools/javac/typeClasses/TypeClassesOperatorResolutionTest.java#L34

After applying the patch, the functionality works as expected and I published a PR taking advantage of the fix:
https://github.com/openjdk/valhalla/pull/1958/files
Thanks.

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PR Comment: https://git.openjdk.org/valhalla/pull/1948#issuecomment-3802811064