Allocator-aware @safe reference counting is still not possible

[Richard (Rikki) Andrew Cattermole]

On 23/01/2023 9:31 PM, Atila Neves wrote:
> On Sunday, 22 January 2023 at 15:50:27 UTC, Richard (Rikki) Andrew 
> Cattermole wrote:
>> On 23/01/2023 4:28 AM, Atila Neves wrote:
>>> [...]
>>
>> I'm not. When I first got a link to that paper I certainly didn't 
>> understand even the basic concepts. Variable based borrow checker is 
>> much easier to understand comparatively.
>>
>> [...]
> 
> I don't understand your post. I've never seen anything resembling the 
> "uncontrolled" above. I think the way to use allocators is via smart 
> pointers/containers and iff it's strictly required.

I have written uncontrolled allocator usage. Its also in druntime/phobos 
plenty. After all its basically just a life cycle is known but compiler 
can't prove anything useful related to it. See any usage of malloc/free 
(including internally to the GC).

But yes, I think the way to go is some sort of controlled representation 
for normal usage (which requires borrowing, which @live does not solve).

```d
Vector!int vector;
vector ~= 3;

auto borrowed = vector[0];
func(borrowed);

void func(scope ref int value) {
	
}
```

Basically right now we're missing the lifetime checks surrounding 
borrowed & function parameter. Everything else is do-able right now, 
even if it isn't as cheap as it could be (like RC eliding).