sumtypes for D

[Per Nordlöw]

On Monday, 28 November 2022 at 09:27:11 UTC, Walter Bright wrote:
> I've written most of a DIP for one. Should I:
>
> 1. submit the DIP
>
> 2. just implement it and do a PR
>
> 3. post the DIP here
>
> 4. wait for a champion to take it over and submit it

Sum-types is the one feature I miss the most in D, so you have my 
blessing. I'm definitely gonna review the DIP.

Btw,

- do you plan on making the sum-type cover nullable-types as a 
special case?
- and is this a preparation for pattern-matching?