There is an important difference for this case though. It C it’s fine to have pointers into uninitialized memory as you as you don’t read them until after initializing. You can write through those pointers the same way you always do. In Rust it’s UB as soon as you “produce” an invalid value, which includes references to uninitialized memory. Everything uses references in Rust but when dealing with uninitialized memory you have to scrupulously avoid them, and instead write through raw pointers. This means you can’t reuse any code that writes through &mut. Also, the rules change over time. At one point I had unsafe code that had a Vec of uninitialized elements, which was ok because I never produced a reference to any element until after I had written them (through raw pointers). But they later changed the Vec docs to say that’s UB, I guess because they want to reserve the right to use references even if you never call a method that returns a reference.