Rust has core::hint::unreachable_unchecked, which is an unsafe function that, since we promised never to call it, also promises never to return. This has Undefi

Rust has core::hint::unreachable_unchecked, which is an unsafe function that, since we promised never to call it, also promises never to return. This has Undefined Behaviour if you call it, since you formally promised not to (the consequence of unsafely promising something and then going back on it is usually Undefined Behaviour in Rust). Rust does also have the safe macro core::unreachable which will panic if reached, but while the compiler can assume this probably won't happen and optimise accordingly, it usually can't know that it won't happen (and if it can your decision to add the macro may be unwise) One reason C++ gets more and more Undefined Behaviour is consistency. The committee will, unless prompted hard not to, draw analogies to existing UB in the language and use that to justify making your new thing Undefined in the tricky cases. The results are pretty embarrassing.