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DidingasLushis: > So basically, this is all still in flux and not currently being worked on? Not saying that is negative, I am just trying to understand where things are at the moment. As a huge fan of pattern types, I hope I'll be lucky enough to see them as a stable language feature in my lifetime. Here's the tracking issue: Tracking Issue for pattern types · Issue #123646 · rust-lang/rust · GitHub A lot of good work has gone into them, but my understanding is we're a very long way from them becoming a thing outside of the compiler (if ever).