Improving DIP74: functions borrow by default, retain only if needed

[Zach the Mystic via Digitalmars-d]

On Friday, 27 February 2015 at 20:30:20 UTC, Steven Schveighoffer 
wrote:
> OK, I found the offending issue. It's when you pass a 
> parameter, the only reference holding onto it may be also 
> passed as well. Something like:
>
> void foo(C c, C2 c2)
> {
>    c2.c = null; // this destroys 'c' unless you opAddRef it 
> before passing
>    c.someFunc(); // crash
> }
>
> void main()
> {
> C c = new C; // ref counted class
> C2 c2 = new C2; // another ref counted class
> c2.c = c;
> foo(c, c2);
> }
>
> How does the compiler know in this case that it *does* have to 
> opAddRef c before calling? Maybe your ARC expert can explain 
> how that works.

Split-passing nested ref-counted classes with null loads! How 
insidious!