> That's exactly how C approaches UB too. In theory yes. In practice it's been proven that's not what happens. > The problem is that's untenable; any nont

> That's exactly how C approaches UB too. In theory yes. In practice it's been proven that's not what happens. > The problem is that's untenable; any nontrivial program will have unsafe somewhere, and unsafe can cause failures arbitrarily far away from the incorrect code. Not really. Ignoring any and all non-compiler tooling, UB in code can be traced to: A) unsafe region in code where its invariants are invalidated B) if no unsafe code exists in project, then an unsoundness bug in the Rust standard lib. Safe code needs to be safe for any possible value of arguments, fields, variables. Doing otherwise is unsoundness bug. In C, the code you need to look is essentially ALL of your code + C std lib. In Rust, you can focus on places where safe and unsafe code mingle. And IFF (if and only iff) your code contains 0 unsafe, can you be sure there is a Rust bug. This however assumes any code. Idiomatic code in Rust will treat unsafe with big large friendly letters `SAFETY: this works while X and Y hold`. How do you do this is C? Since most lines are possible source of UB do you annotate every line of code? I assume not. How do you ensure something will not be mutated? How do you ensure something is thread-safe? Do you use type bounds? And if not how? > If Rust doesn't give you more and better support in doing that than C does, then it's not really making a difference. Also that's the Nirvana fallacy, Rust doesn't have to be perfect and prevent EVERY undefined behavior forever. If it's improvement over the niche it's targeting (C/C++) then it's an improvement. I.e. is it harder to find UB in Rust or in C? Like you don't go around and say, "Well seatbelts don't prevent head injuries when you hit a wall head-on. So remove seatbelts!", you add airbags to cushion the blow. And spoiler alert: It's giving you the airbags as well. The normal thing when encountering a UB isn't to try to track it down it's to run `miri`, it found UB as soon as it ran.