sumtypes for D

[jmh530]

On Wednesday, 30 November 2022 at 13:45:09 UTC, Paul Backus wrote:
> [snip]
>
> - User-defined implicit conversions.
> - Returning error messages from failed `is(...)` and 
> `__traits(compiles)` checks instead of just `false`.
> - Allowing library code to *display* its own custom error 
> messages, with the same control and flexibility the compiler 
> has for built-in messages (currently we only have `static 
> assert`).
> - User-defined GC scanning for library types (`opGCScan`?).
> - User-defined value ranges for aggregate fields (e.g., pointer 
> that can't be null, integer that can't go above/below a certain 
> limit).
>
> All of these are things that built-in types have access to 
> already, and all of these would have useful applications beyond 
> just sum types.

Not sure what is meant by the above about template type 
inference, but here are enhancement requests for what Paul 
mentioned.

https://issues.dlang.org/show_bug.cgi?id=23523
https://issues.dlang.org/show_bug.cgi?id=23527
https://issues.dlang.org/show_bug.cgi?id=23526
https://issues.dlang.org/show_bug.cgi?id=23525
https://issues.dlang.org/show_bug.cgi?id=23524

Feel free to add more info there to further explain what you are 
looking for.