Why do immutable variables need reference counting?

[user1234]

On Sunday, 10 April 2022 at 23:05:24 UTC, norm wrote:
> Hi All,
>
> I am clearly misunderstanding something fundamental, and 
> probably obvious :D
>
> Reading some of the discussions on __metadata I was wondering 
> if someone could explain why a immutable reference counting 
> type is needed. By definition a reference counter cannot be 
> immutable, so what would be the use case that requires it? It 
> cannot really be pure nor safe either because the ref goes out 
> of scope and the allocation is freed. How is this immutable?
>
>
> Thanks,
> Norm

refcounting would require a concept of "tail const" / "tail 
immutable" so that transitivity of the qualifier does not affect 
the data used to refcount (basically the field that hold the 
count) but only the data that **are** refcounted.