> This post describes the idea of a “never pattern” (written !) that matches against the ! type or any other “empty enum” type. It also describes an auto-never transformation that inserts such patterns into matches. As a result – in the desugared case, at least – we no longer use the absence of a match arm to designate matches against uninhabited types.

> Explicit ! patterns make it easier to define what data a match will access. They also give us a way to use lints to help bridge the needs of safe and unsafe code: we can encourage unsafe code to write explicit ! patterns where they might help document subtle points of the semantics, without imposing that burden on safe code.