The main issue in C and C++ is that them aliasing rules are based on types, and the other aspects of the rules make type punning by casting pointers undefined behaviour no matter how valid either type is for a given region of memory. Rust actually does allow type punning through the obvious routes of std::mem::transmute or the same casting of raw pointers. It's wildly unsafe, and you need to have done your homework on whether the pointers represent valid states for the type you're punning to (right layout, alignment, and values), but it's defined behaviour if you're following those rules (one reason being that the lifetimes of the two references don't ever overlap in rust's model). In C and C++ you need to follow all those rules but also you need to jump through some extra hoops with the right incantations, just a pointer cast will be undefined behaviour even if you got everything else right.

(whats 100% not-OK in Rust is casting away constness. If you have a '&T' you must not touch, on pain of a thousand bugs)