NSComparisonMethods / compare:

[David Ayers]

Hello,

I just noticed that new compatibility methods were added to -base which
use the compare: method in their NSObject implementation.

>From memory using compare: on "incompatible" types is undefined
behavior. I.e. a compare: method may assume that the the argument is of
"compatible" class and may reference instance variables of the parameter
directly.  In fact our NSString implementation assumes that.

I haven't found any documentation about this requirement, and I'm not
sure it exists on Cocoa.

But I wonder whether we should document this requirement (i.e. that it's
the users responsibility to insure that the compared objects are
"compatible", since I keep running into such issues when people use
these values and compare NSStrings with NSNumbers or NSNull instances
resulting in invalid memory access.

Cheers,
David

PS: We deprecated NSObject's compare: back in 2003, would anyone mind if
I remove the declaration in our NSObject.h for the following release? [I
would wait another stable release cycle before removing the
implementation.]  Maybe the same should be done for the other deprecated
methods.