I write a fair bit of C#. It feels like the prequal to Typescript. Its lack of discriminated unions and type narrowing feels like a step back from Typescript.

Given that TypeScript is driven in late part by one of the main long term (until they moved to TS) C# language designers, I feel a lot of the core of the TS type system is what they wanted to do in C# but for legacy reasons just can’t.

DU is available in C# via packages like OneOf and Dunet.

Dunet is really good.

https://github.com/mcintyre321/OneOf

https://github.com/domn1995/dunet

It's on the roadmap and will arrive at some point:

https://github.com/dotnet/csharplang/blob/main/proposals/dis...