My Reference Safety System (DIP???)

[Zach the Mystic via Digitalmars-d]

On Friday, 27 February 2015 at 23:18:24 UTC, Marc Schütz wrote:
> I think I have an inference algorithm that works. It can infer 
> the required scope levels for local variables given the 
> constraints of function parameters, and it can even infer the 
> annotations for the parameters (in template functions). It can 
> also cope with local variables that are explicitly declared as 
> `scope`, though these are mostly unnecessary.
>
> Interestingly, the rvalue/lvalue problem deadalnix found is 
> only relevant during assignment checking, but not during 
> inference. That's because we are free to widen the scope of 
> variables that are to be inferred as needed.
>
> It's based on two principles:
>
> * We start with the minimum possible scope a variable may have, 
> which is empty for local variables, and its own lifetime for 
> parameters.
> * When a scoped value is stored somewhere, it is then reachable 
> through the destination. Therefore, assuming the source's scope 
> is fixed, the destination's scope must be widened to 
> accommodate the source's scope.
> * From the opposite viewpoint, a value that is to be stored 
> somewhere must have at least the destination's scope. 
> Therefore, assuming the destination's scope is fixed, the 
> source's scope needs to be widened accordingly.
>
> I haven't formalized it yet, but I posted a very detailed 
> step-by-step demonstration on my wiki talk page (nicer to read 
> because it has syntax highlighting):
> http://wiki.dlang.org/User_talk:Schuetzm/scope2

I need to sleep as well right now. But I still don't understand 
where the cycles come from. Taken from your example:

*b = c;
// assignment from `c`:
// => SCOPE(c) |= SCOPE(*b)
// => DEFER because SCOPE(*b) = SCOPE(b) is incomplete

`c` is merely being copied, but you indicate here that it will 
now inherit b's (or some part of b's) scope. Why would c's scope 
inherit b's when it is merely being copied and not written to?