Want reasonable reference counting? Disable automatic sharing of immutable

[Elronnd]

On Sunday, 14 November 2021 at 18:24:00 UTC, Timon Gehr wrote:
>> 1. ref counted objects are mutable
> Works, but you may have to extend it to "anything that's not 
> allocated with the GC is mutable".

Static data can be immutable too.


>> 2. ref counted objects are outside of the type system
> For this to work, there still needs to be a careful definition 
> what @trusted functions are allowed to do with data of certain 
> qualification. I think adding some type system support that is 
> strictly @system, like __mutable variables and functions is 
> better than having no language support at all, because 
> otherwise, in order to support reference counting, you may end 
> up penalizing code that does not actually use it.

I assumed that 'outside of the type system' meant 'language-level 
support for reference counting'; a a type with opaque 
representation, like a hash table.


>> PS. I suspect that ref counted shared mutable objects are an 
>> indicator of insanity.
> Possibly, though it's hard to know everyone's use cases in 
> advance.

GC really makes more sense for multithreaded programs.  Travis 
downs mentions at 
https://travisdowns.github.io/blog/2020/07/06/concurrency-costs.html.  IMO if you are sharing mutable data between threads, and you can't stand gc for some reason, then it's perfectly legitimate to make you manage the lifetime yourself.