Want reasonable reference counting? Disable automatic sharing of immutable

[Steven Schveighoffer]

On 11/12/21 6:32 PM, Ola Fosheim Grøstad wrote:
> On Friday, 12 November 2021 at 23:07:02 UTC, Steven Schveighoffer wrote:
>> The problem is of course that this is not pure. As long as you don't 
>> need pure reference counting, it's a possible solution.
>>
>> If you do need pure reference counting, this mechanism *cannot* be 
>> used, even if it's not technically accessing a global. I don't care 
>> what tricks you want to pull, the optimizer is going to bite you for it.
> 
> Not if it is built in. Anyway, you can just require all functions to 
> take the counter table as a parameter, by rewriting rules, that makes it 
> pure even when it isn't builin.

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.

>> 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.

-Steve