Enumerated Unions (sum types)

[Paul Backus]

On Thursday, 12 September 2024 at 10:32:39 UTC, Dukc wrote:
> On Thursday, 12 September 2024 at 09:56:44 UTC, Paul Backus 
> wrote:
>>> Also I propose that the tag type is enumerated type that is 
>>> implicitly convertible to `int`. The base type is an unsigned 
>>> integer type big enough to hold all the field types. Default 
>>> value and the enumerated values (other than having one for 
>>> each type) can remain unspecified though.
>>
>> By "tag type" I assume you mean the type of the __tag 
>> property. Is there any practical difference between what you 
>> describe and just using size_t?
>
> Well, `size_t` takes more space. Then again, if the tag 
> property would be a getter as opposed to a direct field 
> accessor the tag type wouldn't necessarily have to match with 
> the real type of the tag field, in which case there's no 
> difference.

`__tag` is an rvalue property, and the intent is that the 
`size_t` it returns can be computed at runtime from the data 
stored in the tag field. It's analogous to SumType's `typeIndex` 
method.