Or maybe a heavyweight one. I note that the clang annotations refer to "typestate", which was a mechanism that existed in primordial Rust, but which was dropped

Or maybe a heavyweight one. I note that the clang annotations refer to "typestate", which was a mechanism that existed in primordial Rust, but which was dropped because it was unnecessarily complicated: http://pcwalton.github.io/2012/12/26/typestate-is-dead.html http://pcwalton.github.io/2012/12/26/typestate-is-dead.html Although to be fair, clang's version is a highly limited particular case of typestate, with one axis of state with three values, rather than a general heavyweight typestate mechanism.