The C# team for several reasons decided "rock solid" pattern matching was a higher priority than discriminated unions because good discriminated union code needs good pattern matching. In the last few versions of C# I think pattern matching has gotten really good. List Patterns finally exist now, and that influenced the new iterable collection initializers, which are also pretty good now. Last I checked, the C# team was still debating Dictionary/Hash key lookup Patterns and Dictionary/Key-Value initializers, and that's maybe my last big request in pattern matching other than native discriminated unions, of course.