Cocoa Grandfather

Question

Is it possible to access the super class method of an objects super class (or grandfather)?

For instance:

GrandFatherObject : NSObject
SuperObject : GrandFatherObject
SelfObject : SuperObject

From SelfObject:

- (void)overriddenMethod
{
  // For Self
  someCode();

  // For Parent
  [super overriddenMethod];

  // For GrandParent
  ???
}

I only have access to SelfObject (Can't modify SuperObject or GrandFatherObject)

Answer 1

Why would you want to do this? You should rethink your class design if you think this is necessary. You can always, of course, call super in the parent class's implementation of overriddenMethod.

For proper encapsulation, subclasses shouldn't need to know about anything other than their parent class. Otherwise you have tight, bi-directional coupling within the inheritance hierarchy. Nightmares.

Answer 2

Yes, you can do it, but it takes a bit more code than just invoking super.

More or less, it'd be something like this:

#import <objc/runtime.h>

struct objc_super grandsuper;
grandsuper.receiver = self;
grandsuper.class = class_getSuperclass(class_getSuperclass([self class]));

//if _cmd has a non-struct return value:
id grandsuperReturnValue = objc_msgSendSuper(&grandsuper, _cmd, arg1, arg2, ...);

Answer 3

While playing with objc_msgSendSuper() is certainly fun, why don't you take the easy way and create a Category in the SelfObject implementation, something like

@interface SuperObject (ForSelfObject)
  - (id)grandFatherOverridenMethod;
@end

@implementation SuperObject (ForSelfObject)
  - (id)grandFatherOverridenMethod {
    return [super overridenMethod];
  }
@end

You said you can't modify SuperObject, that doesn't mean you can't extend it. Am I missing any major drawbacks here?