Are these things HN readers didn't know?

I didn't know you can do operator overloading in Java (with Manifold). That would be interesting: https://www.youtube.com/watch?v=pwQs-308OdY

I was not aware of manifold; from a quick look, my understanding is that manifold is a bunch of popular language extensions, implemented mostly via preprocessor annotations, which are highly tied to specific java versions and IDEs.

But while that does seem cool, I'd hesitate to call manifold-driven operator overloading as "modern java supporting op overloading". To me it has the same vibe as simulating high-level syntax in c via hacky macros.

That's not how it works exactly. It's a deep integration as a compiler plugin extension. It works with LTS versions since 8 and with Java 19 (I think 20 also works but not sure).

Modern Java is the title of the series that talks about many different subjects including new Java language features, etc.

As in, the java compiler formally provides extension APIs, and Manifold taps directly into those?

Hm, ok, in that case, slightly less hacky. Probably more comparable to using gcc extensions then... in that, I'd still hesitate to call it "this is evidence that c supports x" ... but it's the kind of statement that could be argued both ways, and discussions would probably quickly devolve into semantics and pedantry rather than anything of practical significance.

It's very impressive and far bigger than the operator overloading stuff. The other videos in that series cover some of the other features.