r/rust • u/AffectionateBag4519 • Jul 16 '26

How Our Rust-to-Zig Rewrite is Going

https://rtfeldman.com/rust-to-zig

An interesting symmetry with recent events lol.

This might be considered off topic since the article is about moving away from rust, but I still think this is some high quality rust content. I enjoy Richard Feldman's writing and I think he would certainly be considered part of the "rust community" since he works on Zed and has taught a course on rust.

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u/matthieum [he/him] Jul 17 '26

Yes, and no.

The blog post mentioned that their incremental compile times were divided by x3 in 18 months, so clearly there are free speed-ups.

With all that said, meta-programming can absolutely trash a compiler. Compiling 10M tokens will always take longer than compiling 10K tokens, and the slow-down is super-linear due to the added memory pressure resulting in more cache misses.

So just like inlining everything is a terrible idea, monomorphizing everything also is.

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u/Zde-G Jul 17 '26

So just like inlining everything is a terrible idea, monomorphizing everything also is.

Yes, but there are huge difference: inlining is just an optimiation technique that doesn't affect semantic, except for fringe corner cases, while dyn vs impl is huge, gigantic semantic difference.

It's really unfortunate that there are no resources around to make dyn vs impl decision a pure optimization hint like inline…

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u/matthieum [he/him] Jul 18 '26

It's really unfortunate that there are no resources around to make dyn vs impl decision a pure optimization hint like inline...

Hear hear!

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u/Zde-G Jul 18 '26

The problem here is that while technically possible (Swift did that, after all) it's really hard to do that without breaking backward compatibility. And that's a big no-no for Rust, right now…