I'm actually surprised their example wasn't the accidental use of a valid ID, not an invalid one. An invalid one is easily catchable, but an invalid one is akin

I'm actually surprised their example wasn't the accidental use of a valid ID, not an invalid one. An invalid one is easily catchable, but an invalid one is akin to a bad pointer. The resulting behavior will slip by the Rust compiler, as we're basically using integers as pointers, and you can get all sorts of shadow-clone versions of malignant pointer behavior like use-after-free in such a scheme. That said … there are ways in Rust to do circular data structures that don't have the problems that using indexing into an array has, and are memory safe, and are within the safe subset of Rust. (E.g., Rc/Arc.)