[andrepd]

Rust has assert and debug_assert, which are self-explanatory. But it also has an assert_unchecked, which is what other languages incl C++ call an "assume" (meaning "this condition not holding is undefined behaviour"), with the added bonus that debug builds assert that the condition is true.

[tialaramex]

Notably, like most things with "unchecked" in their name `core::hint::assert_unchecked` is unsafe, however it's also constant, that is, we can do this at compile time, it's just promising that this condition will turn out to be true and so you should use it only as an optimisation.

Necessarily, in any language, you should not optimise until you have measured a performance problem. Do not write this because "I think it's faster". Either you measured, and you know it's crucial to your desired performance, or you didn't measure and you are wasting everybody's time. If you just scatter such hints in your code because "I think it's faster" and you're wrong about it being true the program has UB, if you're wrong about it being faster the program may be slower or just harder to maintain.