std.sumtype?

[Oleg B]

On Tuesday, 23 March 2021 at 14:45:18 UTC, Atila Neves wrote:
> On Friday, 19 March 2021 at 07:28:19 UTC, drug wrote:
>> On 3/18/21 9:42 PM, Oleg B wrote:
>>> 
>>> but read-only tag (kind, type index) is key feature in chouse 
>>> between sumtype and other for me, and I hope it will be added 
>>> before next compiler release...
>>> 
>>
>> Totally agree, it is an important feature.
>
> Can anyone explain to me why?

Simple general example is serialization and deserialization of 
algebraic value: without tag (kind, type index) it's not 
impossible but more complicated. For serialization you need write 
tag first (`match` is good for serialization exist value) and 
then deserialize you need to read tag and do deserialization for 
writed value type (how it must be with `match`?). If tag is 
private and/or it not direct point to types you need "jump 
through hoops" for this simple algo.