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Comment by CuriouslyC | Hacker News Reader

I've been genuinely surprised how well GPT5 does with rust! I've done some hairy stuff with Tokio/Arena/SIMD that I thought I would have to hand hold it through, and it got it.

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Yeah, it has been really good in my experience. I've done some niche WASM stuff with custom memory layouts and parallelism and it did great there too, probably better than I could've done without spending several hours reading up on stuff.

It's pretty good at Rust, but it doesn't understand locking. When I tried it. It just put a lock on everything and then didn't take care to make sure the locks were released as soon as possible. This severely limited the scalability of the system it produced.

But I guess it passed the tests it wrote so win? Though it didn't seem to understand why the test it wrote where the client used TLS and the server didn't wouldn't pass and required a lot of hand holding along the way.

I've experienced similar things, but my conclusion has usually been that the model is not receiving enough context in such cases. I don't know your specific example, but in general it may not be incorrect to put an Arc/Lock on many things at once (or using Arc isntead of Rc, etc) if your future plans are parallelize several parts of your codebase. The model just doesn't know what your future plans are, and in errs on the side of "overengineering" solutions for all kinds of future possibilities. I found that this is a bias that these models tend to have, many times their code is overengineered for features I will never need and I need to tell them to simplify - but that's expected. How would the model know what I do and don't need in the future without me giving all the right context?

The same thing is true for tests. I found their tests to be massively overengineered, but that's easily fixed by telling them to adopt the testing style from the rest of the codebase.

Rust has been an outlier in my experience as well. I have a pet theory that it is due to rust code that's been pushed to github generally compiles. And if it compiles it generally works.

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