Question

I have the following inheritance tree:

NSObject <- GameObject <- RenderableObject <- SimpleBullet

GameObject has a method called bounds that returns the object’s bounds. In my code I have a SimpleBullet that calls bounds to get its bounds, and I receive a warning saying bounds is defined in several places; odd. If I cast the SimpleBullet to a GameObject and call the bounds method, everything works as expected. What’s happening? I can’t figure out this behaviour. Example:

SimpleBullet* bullet = bulletInstance;
[bullet bounds];    // we get the warning.
[(GameObject*)bullet bounds];    // works as expected.

As I said, the bounds method is defined in GameObject, but why is Obj-C not aware that SimpleBullet is a GameObject and not allowing me to call its method without the warning?

Answer 1

After some investigation I managed to know what was happening. The compiler was playing tricks on me because did not report a meanfull error. The problem was that I wasn’t importing/including SimpleBullet.h. A forward declaration was declared but not the real implementation.

This, leads me to think that by default compiler treats it as an id object, and tries to find a method among all registered classes that suits the call signature. Just a guess, not sure about this :).

Thanks for all the help.