alt Hacker NewsYou seem to have been misinformed. Rust panics on overflow in debug mode (or always if you toggle a compiler flag), and has a guaranteed wrap-around in release mode. In no case there is UB.
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No, that's exactly what I'm aware of, and is exactly the wrong behavior I'm talking about. "Sometimes crashes, sometimes two's compliment" are extremely different behaviors, and not meaningfully different from just saying it's UB. It should always panic, with no way to disable it. The wrap around in release mode is simply bad behavior. It can't be relied upon (because it panics in debug), and it's not useful behavior for nearly anyone's logic (wrap around almost never is logically correct behavior)
It lets Rust claim to be UB free without delivering the actual value of being UB free. You still can't rely on a given behavior because it doesn't have one behavior, it has two, and the two behaviors are wildly incompatible with each other.
Supporting evidence for this: https://doc.rust-lang.org/book/ch03-02-data-types.html#integ...