Want reasonable reference counting? Disable automatic sharing of immutable

[Stanislav Blinov]

On Sunday, 14 November 2021 at 00:17:29 UTC, Elronnd wrote:
> On Saturday, 13 November 2021 at 23:08:01 UTC, Stanislav Blinov 
> wrote:
>> Read `a`, call pure function, read `a`. Where is it possible 
>> for `a` to mutate, after first read and before second read? 
>> Can't be the pure function, it's pure and cant mutate `a`. So
>> where is it possible for `a` to mutate?
>
> auto x = new int;
> assert(a < 5);
> auto y = new int;
> assert(a < 5);
> *x += *y;
>
> Would you begrudge the compiler the ability to remove the 
> second assert?  Because there is the _exact_ same problem there.

So long as collection can call any destructors indiscriminately - 
yes, I would. Because with current runtime and GC spec `a` might 
mutate in either call to `new`. Even in both.

> Actually, forget allocation.  A signal can occur at _any_ time, 
> and its handler can change globals.

Indeed, forget allocation, given that I'm talking about 
collection. But anyway, so what? What do signals have to do with 
`new` pretending to be pure when it calls destructors that aren't?

>> Can't be another thread, `a` is a thread-local int.
>
> You can share pointers to thread-local objects.

Indeed you can. How does that apply here?