A proposal for type unions (aka discriminated unions) in C#

From the meeting minutes:

First up today, the discriminated unions working group presented the proposal they've been working on for a while to the broader LDM. This was a broad overview session, rather than a deep dive into nitty-gritty questions; there are still plenty of little details that will need to be filled in, but we're cautiously optimistic about this proposal and moving forward with it. There was some concern about some of the ternary behavior, but we can dig more into that as we bring this proposal back for detailed follow ups in the future.