On Oct 10, 2008, at 5:40 PM, Ian Joyner wrote:
I'm just trying to work out what NSNull really is in the Cocoa
context. Is it an object in Cocoa?
As I said, yes. It's truly an object. (A singleton, as well.)
Since NSNull may be a "valid" value of any other type, is it counted
as a subtype of every other type (hence the ultimate subclass)? I
think a good and simple (one that doesn't make my brain hurt)
definition of NSNull is important in order to ensure software
correctness.
Woah. Talk about brain hurt. You're thinking about this far too much.
There's no inheritance, there's no nothing. It's an object. It's
absolutely in no way different than you creating your own IJNull
class, and sticking an instance of it anywhere. It doesn't behave any
differently.
As for use, the documentation says it pretty clearly:
"The NSNull class defines a singleton object used to represent null
values in collection objects (which don’t allow nil values)."
You can't stick nil into dictionaries and arrays. So either you stick
an empty string, an NSNumber with 0, etc if those are OK, or you can
use NSNull.
--
Seth Willits
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