draft proposal for Sum Types for D

[Paolo Invernizzi]

On Wednesday, 30 November 2022 at 09:33:54 UTC, Walter Bright 
wrote:
> On 11/29/2022 12:37 PM, Per Nordlöw wrote:
>> ```d
>> sumtype Result
>> {
>>      Error,
>>      int Value
>> }
>> ```
>> 
>> , is
>> 
>> ```d
>> Result res;
>> res = 25;
>> ```
>> 
>> supposed to be supported aswell?
>
> At the moment, no, should be:
>
>      res.Value = 25;
>
>
>> If so, why not
>
> I'd reframe that as why do it?
>
> On a pragmatic note, there may be multiple matches for an int 
> in the sumtype.

I would have preferred a sumtype more similar to a functional 
language custom type (like in 'Elm'), where every member must be 
of a different type, just to allow what Per was asking.

/Paolo