Re: ARC Cleanups

[Nicola Pero]

> With ARC, the runtime needs to be able to find the reference count for the 
> fast path,
> so this becomes part of the interface between the runtime and Foundation, and 
> so has
> to be stable.  If we keep the order refcount, zone, isa, then we can't remove 
> the zone
> pointer without breaking the ABI.  If we change the order to zone, refcount, 
> isa, then
> the interface is just refcount, isa, and we can delete the zone in the future 
>  if we want,
> or keep it if it makes sense.

Yes, it makes sense, and it would be good to have a simple and stable ABI. :-)

Btw, if we're changing everything, I wonder if we shouldn't even make these 
normal
instance variables ... then, the ABI for the runtime would be really simple ... 
the
first instance variable would be the class ('isa'), and the second one would be 
the
retain count.  The third one would be the zone, and the runtime can ignore that.

I can think of a number of problems and complications with this, so I'm not 
sure it would
be a good idea, but it's worth considering. ;-)

Thanks