On 09/08/2012, at 9:39 AM, Greg Parker <gpar...@apple.com> wrote:
> NSCopyObject() is ugly. Avoid it if you can.
>
> NSCell uses NSCopyObject. I don't know if there are other framework classes
> that are likely to be copied and subclassed that use NSCopyObject.
>
> One solution is to compile your subclass with ARC. ARC-compiled ivars get
> correct retain count management inside NSCopyObject. (You still need to
> override -copyWithZone: if you want those ivars to be copied instead of
> retained, though.)
I see that NSCopyObject is deprecated as of 10.8 (but is still being used
internally).
This is going to be fun moving forward :) I'm not sure how binary compatibility
is going to be maintained as NSCopyObject disappears, for example, in a cell
subclass I might have:
- (id) copyWithZone:(NSZone*) zone
{
MyCell* copy = [super copyWithZone:zone];
[copy->someInternalPointer retain];
return copy;
}
This relies on the existing behaviour of NSCopyObject not retaining pointers it
has copied.
If in future NSCell changes to use some alternative such as the ARC stuff you
mention, this will now leak due to the extra retain. If I don't do the retain,
it will crash on older systems due to the (later) over-release.
Is there a solution to this that will work forwards and backwards?
Incidentally I did find buried in an insignificant corner of the documentation
that NSCell only copies pointers, in "Subclassing NSCell": "If the subclass
contains instance variables that hold pointers to objects, consider overriding
copyWithZone: to duplicate the objects. The default version copies only
pointers to the objects". IMHO this should be in huge red letters in the NSCell
class reference, with its consequences properly spelt out.
--Graham
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