Whoa - maybe I've had too much wine with dinner, but:
Is it really true what Jens says, that [[NSArray alloc]init] always
returns the same pointer?
If that is the case, how can one declare two separate arrays?
Jeff
On Sep 21, 2016, at 8:50 PM, Jens Alfke wrote:
> On Sep 21, 2016, at 6:36 PM, Graham Cox <graham....@bigpond.com> wrote:
>
> Which is yet another reason why void* is such a shitty concept. Apple could
> easily have insisted that parameter was id<NSObject> without any real
> problems, so void*… sheesh.
It’s not an object! It’s just an opaque ‘cookie’ that you can use to recognize
which observer is being invoked, and specify which one to remove.
The point of using a void* is that it’s easy to generate guaranteed-unique
values by taking the address of a static variable. If the context were an
object, people would be likely to assume they should use -isEqual: to compare
them (as half the people on this thread seem to be doing), but that’s not a
good idea because it can result in false positives comparing
equal-but-different objects.
Moreover, it can be hard to be sure whether you’re getting distinct objects in
Obj-C, since initializers will often return unique singletons for common cases.
For instance, [[NSArray alloc] init] will always return the same pointer every
time it’s called, making it a terrible choice for a context.
—Jens
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