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by kibwen 77 days ago
No, this is false. For Rust codebases that aren't doing high-peformance data structures, C interop, or bare-metal stuff, it's typical to write no unsafe code at all. I'm not sure who told you otherwise, but they have no idea what they're talking about.
2 comments
crote 77 days ago
It's the classic "misunderstanding" that UB or buggy unsafe code could in theory corrupt any part of your running application (which is technically true), and interpreting this to mean that any codebase with at least one instance of UB / buggy unsafe code (which is ~100% of codebases) is safety-wise equivalent to a codebase with zero safety check - as all the safety checks are obviously complete lies and therefore pointless time-wasters.

Which obviously isn't how it works in practice, just like how C doesn't delete all the files on your computer when your program contains any form of signed integer overflow, even though it technically could as that is totally allowed according to the language spec.

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zozbot234 76 days ago
If you're talking about Rust codebases, I'm pretty sure that writing sound unsafe code is at least feasible. It's not easy, and it should be avoided if at all possible, but saying that 100% of those codebases are unsound is pessimistic.

One feasible approach is to use "storytelling" as described here: https://www.ralfj.de/blog/2026/03/13/inline-asm.html That's talking about inline assembly, but in principle any other unsafe feature could be similarly modeled.

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crote 76 days ago
It's not impossible, it is just highly unlikely that you'll never write a single safety-related bug - especially in nontrivial applications and in mixed C-plus-Rust codebases. For every single bug-free codebase there will be thousands containing undiscovered subtle-but-usually-harmless bugs.

After all, if humans were able to routinely write bug-free code, why even worry about unsoundness and UB in C? Surely having developers write safe C code would be easier than trying to get a massive ecosystem to adopt a completely new and not exactly trivial programming language?

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zozbot234 76 days ago
Rust is not really "completely new" for a good C/C++ coder, it just cleans up the syntax a bit (for easier machine-parsing) and focuses on enforcing the guidelines you need to write safe code. This actually explains much of its success. The fact that this also makes it a nice enough high-level language for the Python/Ruby/JavaScript etc. crowd is a bit of a happy accident, not something that's inherent to it.
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bluGill 76 days ago
Our experiences are different.

Good developers only write unsafe rust when there is good reason to. There are a lot of bad developers that add unsafe anytime they don't understand a Rust error, and then don't take it out when that doesn't fix the problem (hopefully just a minority, but I've seen it).

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