Want reasonable reference counting? Disable automatic sharing of immutable

[Ola Fosheim Grøstad]

On Friday, 12 November 2021 at 18:12:14 UTC, Andrei Alexandrescu 
wrote:
> We discussed this a couple of times. It's interesting. Sadly at 
> this point implicit thread sharing of immutable is so baked 
> into the language, it would take a lot of care to extricate. It 
> would be very difficult even for Timon or Paul.

Just define a new keyword for unshared immutable and make 
"immutable" an alias.