WeakRefs for a CPP->D wrapper

[Abdulhaq]

>
> No, try this:
> import std.stdio;
> class X {}
> void foo(X x) { writeln(cast(void*) x); }
>
> void main() {
>          X x; // null reference by default.
>          writeln(cast(void*) x);
>          foo(x);
>
>          x = new X;
>          writeln(cast(void*) x);
>          foo(x);
> }

Thanks Tobias that indeed works, unfortunately storing the 
address as ulong in an AA does not seem to be defeating the 
garbage collector!

I guess I'll have to go for a WeakRef implementation, I'll try 
Robert's implementation in signals, but I'd really like to know 
how long it is likely to last as a working weak ref (in terms of 
the D GC changing etc.) and if I'm taking the right approach.