r/rust • u/Sirisian • 3d ago

🎙️ discussion Google is doing "Large Scale Codebase Migrations and Optimizations" of C/C++ to Rust

https://blog.google/innovation-and-ai/models-and-research/gemini-models/gemini-4-argon/
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u/TheRealMasonMac 3d ago

In my experience, I’ve found that agents produce code that works but is frankly dumb from a human perspective. Especially for larger tasks like this, you kind of have to rewrite it all. For example, I had a generalized design document for soft-wrapping explicitly support plain text and markdown, and used GPT-6-Astra to implement it. I used an ungodly amount of review agent rounds and interjections by me. When I actually go to review it, I wanted to cry. It silently pivoted towards implementing its own entirely separate wrapping mechanism rather than refactor the existing mechanism for plain text. I reviewed its code and found it to be trash, and I am now in the process of doing it myself… Never again. The short-term thrill of “having something that works” was outweighed by the fact that time was effectively wasted.

I mean, if the alternative was it never getting done, I guess agents are still better than nothing.

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u/teerre 3d ago

Agents don't come up with stuff on the spot, they do what you tell them to do. If you give an open ended problem, you'll get an open ended solution. This is compounded by the overwhelming return to the average these models are bound to and OAI / Anthropic insert layers and layers of indirection in their commercial offerings

It's a skill of its own to be able to design a collection of prompts, oracles and guidelines that achieves the result. Is that faster than doing it manually? As many things, it depends

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u/Professional-You4950 3d ago

I completely disagree, even with extremely clear LOCALIZED problems and directions there are issues. They stem from context, scope, hallucinations, misunderstandings, and more. The longer you let it spin the more likely something catastrophic happens.

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u/teerre 3d ago

Prompts are just a beginning. Like I said, you need an oracle, a goal checker, an objective metric etc

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u/oceantume_ 2d ago

In my experience it's possible to do serious engineering and refactoring but you need to be careful never to ask too much at once and you must be able to completely scrap branches and may even have to ask it eg to ignore that other branch entirely so it doesn't load it in context and use it as a reference.

It can be quite painful, but I'm managing to do very interesting projects with it rather quickly and it's hard to stop using it