std.sumtype?

[Steven Schveighoffer]

On 3/18/21 12:11 PM, Paul Backus wrote:
> On Thursday, 18 March 2021 at 15:58:55 UTC, Oleg B wrote:
>> auto tag = val.match!(
>>   (Type1 t1) => 0, // or MyOwnValTag.type1
>>   (Type2 t2) => 1, // or MyOwnValTag.type2
>>   ... etc
>> );
>>
>> next write tag, in next match write value
>>
>> how to generate this match without mixins? how to get (in general way) 
>> type from sumtype val by own tag or number for deserialization?
> 
> Something like this:
> 
> alias QualifiedTypes = CopyTypeQualifiers!(typeof(val), val.Types);
> auto tag = val.match!(v => staticIndexOf!(typeof(v), QualifiedTypes));

Wait, you can't access the tag for the tagged union?

FYI, taggedalgebraic, it's simply val.kind.

I'd suggest giving read-only access to the tag. The types are already 
accessible.

-Steve