Want reasonable reference counting? Disable automatic sharing of immutable

[Ola Fosheim Grøstad]

On Friday, 12 November 2021 at 23:50:15 UTC, Steven Schveighoffer 
wrote:
> That means every pure function must be passed the global table 
> as a parameter *just in case* there are some reference-counting 
> things to do, and that means that no pure function can be 
> strong-pure. Might as well not have pure functions in that case.

Depends on how you define pure.

Is it a tool for compiler optimizations? Not a problem. The 
compiler knows the invariants for reference counting.

Is it a tool to make it easier for programmers to reason about 
programs. Clarfy in the sec what you can assume.

Do you want the compiler to check strong purity? Define it. Make 
it possible to express it and let the compiler check it.

If you require pure to mean that no life times are extended, say 
so in the spec and let the compiler check it.

>>> I'm skeptical that even normal optimizations outside of pure 
>>> won't bite you on this either.
>> 
>> If it is builtin then optimizations cannot be a concern?
>
> As I said, I'm skeptical, I'm not sure if some optimization 
> somewhere isn't going to make hay with our cleverness. We have 
> smart people working on the compilers, so I'll leave the 
> judgment up to them.

An compiler optimization cannot create problems, by definition, 
as it does not change the language. If it creates problems then 
it means that the language specification is in need of fixing. Or 
that that the programmers assume things that the language does 
not guarantee.