[cfe-dev] Even more clang ideas
cmh at me.com
Sat Jul 26 02:02:40 CDT 2008
On Jul 25, 2008, at 6:28 PM, Ted Kremenek wrote:
>> It is, in fact, an error to return a NSMutableArray in a method
>> that's prototyped to return an NSArray due to C pointer aliasing
>> rules. The 'id' type is the closest thing that Objective-C has to a
>> 'generic object pointer type', so if a method wants to return a
>> pointer to an object of more than one type, it really should declare
>> the return type as 'id'. Again, this is due to the C pointer
>> aliasing rules rather than any OO conceptual rules.
> Again, I'm not certain how much C99's aliasing rules apply to
> Objective-C object references. Objective-C doesn't have a formal
> specification akin to C99, so the specification (if you want to call
> it that) is whatever the current compiler implementation allows.
The current specification of Objective-C is "The Objective-C 2.0
Programming Language" at <http://developer.apple.com/documentation/Cocoa/Conceptual/ObjectiveC/
John is also incorrect about the above: It is *not* an error, in
Objective-C, to return an instance of a subclass from a method
prototyped as returning an instance of the superclass.
Objective-C is its own language that extends C99, not a preprocessor
for C99, and this is one of the extensions that Objective-C adds. In
fact, in Objective-C it is not possible to say "this method returns an
instance of specifically this class and no other class" -- you can
only say "this method returns an instance of this class or any
That is by design, and is not just an artifact of its original
mid-1980s implementation as a preprocessor.
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