On Fri, May 23, 2008 at 5:11 PM, Sherm Pendley <[EMAIL PROTECTED]> wrote: > On Fri, May 23, 2008 at 4:45 AM, Michael Ash <[EMAIL PROTECTED]> wrote: >> >> On Fri, May 23, 2008 at 4:30 PM, Sherm Pendley <[EMAIL PROTECTED]> >> wrote: >> >> > Does this sound similar? Objective-C obviously already has access >> > limiters, >> > but disassociating the object and property storage would eliminate the >> > last >> > remnants of the fragile base class problem. It would also allow >> > categories >> > to add ivars, would it not? >> >> Categories could only add ivars if they were loaded at the same time >> as the main class, otherwise they could change the size of already >> instantiated objects which is Very Bad. > > That's just the problem that inside-out objects would solve! With the ivars > stored separately from the isa pointer, adding an ivar would simply add > another ivar storage dictionary to the heap. Since inside-out objects are > nothing more than keys into the ivar storage dictionaries, adding another > dictionary doesn't change the size of any objects past, present, or future.
It certainly would solve that problem, but the solution isn't free. Dictionary lookups are significantly more expensive than a direct memory load, especially when you make the dictionaries thread safe and then pound on them a lot from multiple threads. Taking a lock every time I access an ivar doesn't sound very fun to me. This idea is commonly used explicitly to provide ivar-like things in categories. And in fact with the addition of garbage collection this becomes vastly easier to accomplish; your dictionary can simply be an NSMapTable with weak keys, removing the need to do evil swizzling tricks so you can know when objects get deallocated. Mike _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to [EMAIL PROTECTED]
