My Reference Safety System (DIP???)

[deadalnix via Digitalmars-d]

On Monday, 2 March 2015 at 13:30:39 UTC, Zach the Mystic wrote:
> On Monday, 2 March 2015 at 08:59:11 UTC, deadalnix wrote:
>> On Monday, 2 March 2015 at 00:37:05 UTC, Zach the Mystic wrote:
>>>> I'm sure many inc/dec can still be removed.
>>>
>>> Do you agree or disagree with what I said? I can't tell.
>>
>> Yes, but I think this is overly conservative.
>
> I'm arguing a rather liberal position: that only in a very 
> exceptional case do you need to protect a variable for the 
> duration of a function. For the most part, it's not necessary. 
> What am I conserving?

I let the night go over that one. Here is what I think is the 
best road forward :
  - triggering postblit and/or ref count bump/decrease is 
prohibited on borrowed.
  - Acquiring and releasing ownership does.

Now that we have this, let's get back to the exemple :
class C {
     C c;

     // Make ti refconted somehow, doesn't matter. Andrei's 
proposal for instance.
}

void boom() {
     C c = new C();
     c.c = new C();

     foo(c, c.c);
}

void foo(ref C c1, ref C c2) {
     // Here is where things get different. c1 is borrowed, so you 
can't
     // do c1.c = null before acquiring c1.c beforehand. That 
means the
     // compiler needs to get a local copy of c1.c, bump the 
refcount
     // to get ownership before executing c1.c = null and decrease
     // the refcount. The ownership expire when the function 
returns
     // so c2 is free when foo returns.
     c1.c = null;
     // c2 is dead.
}

The definition is a bit wonky ATM and most likely needs to be 
refined, but I think this is the way forward with that issue. It 
allow elision of a lot of ref increase/decrease by the compiler, 
which is very important to get refcounting works fast.