OT: (C#) Type Unions for C#

[Quirin Schroll]

On Tuesday, 6 August 2024 at 19:44:12 UTC, Kapendev wrote:
> On Friday, 2 August 2024 at 10:29:22 UTC, ryuukk_ wrote:
>> Some people over here like to take C# as inspiration for new 
>> DIPs
>>
>> Well, tagged union is coming to C#, let's resurrect that old 
>> DIP and go submit a PR
>
> Tagged unions in C# seem quite complex. 🤢
> Maybe the OdinLang implementation might be a better 
> inspiration: https://odin-lang.org/docs/overview/#unions

It seems Odin has type unions. I actually dislike their approach.

IMO, you have two sane approaches:
* Plus-like type sums where order doesn’t matter, duplication 
doesn’t matter and they auto-inline. The empty plus-like sum is 
`noreturn` and adding `noreturn` to a plus-like doesn’t actually 
add it, so that `S+(T+noreturn)` is another way to spell `T+S`.

* Tag-based type unions where order matters, duplication matters 
(different tags), they do not auto-inline, and the empty one is 
at definition site its own type.

 From a plus-based type sum, you extract values asking for a value 
of some type. From a tag-based one, you request by tag.