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The point is that Option in Rust doesn't have undefined behavior in any case, even if the values aren't known at compile time. Exhaustiveness is always checked
by kaashif 2y ago
The point is that Option in Rust doesn't have undefined behavior in any case, even if the values aren't known at compile time. Exhaustiveness is always checked at compile time, unlike C++ where operator* offers an escape hatch where nothing is checked in non-constexpr contexts.
"Make everything constexpr" isn't a real solution to UB, in the same way that "make all functions pure" isn't a solution for managing side effects.
Not adding UB to your APIs, on the other hand, is a real solution.
- School-Cotton 2y agoYou can actually implement the C++ behavior, if you want: unsafe fn super_unwrap<T>(x: Option<T>) -> T { match x { Some(val) => val, None => unreachable_unchecked!(), } } But defaults matter, and Rust certainly doesn’t make this kind of thing ergonomic (which is a correct decision on the Rust designers’ part).
- kaashif 2y agoYeah, absolutely. My point is that Option itself doesn't give you this API and to make an unsafe version, you have to explicitly write it. Including UB in easy to misuse places is totally unnecessary and a footgun which really does cause issues in real code.
- School-Cotton 2y agoYep, I agree completely. Just wanted to point out for completeness that rust can theoretically do the same thing as c++.
- tialaramex 2y agoYou don't have to write this, it already exists as the (unsafe of course) method Option::unwrap_unchecked Because all Rust's methods can be called as free functions, you can literally write Option::unwrap_unchecked for the same behaviour, or you can some_option.unwrap_unchecked() (in both cases you will need to be in unsafe context for this to be allowed and should write a SAFETY comment explaining why you're sure it's correct)
- School-Cotton 2y agoI see. I didn't know that method existed despite spending ~4.5 years writing Rust.
- kaashif 2y agoHa, same. I very very rarely write code in unsafe contexts which is why, I guess.