Re: Use of Mac OS X 10.5 / Leopards Garbage Collection Considered Harmful

FROM : Jean-Daniel Dupas
DATE : Wed Feb 06 18:05:46 2008

>>

>
> Structures don't have "magic invisible members":
>
> @interface Foo {
> }
> @end
>
> Foo *aFoo;
> NSLog(@"Foo is a %@", aFoo->isa);
>
> Notice how there is an "isa" member that is automatically put there, 
> not unlike the way that a C++ object might have a vtable (or other 
> internal plumbing for multiple inheritance).
>



Wrong. This will not work. Foo will not have a magic isa ivar, an is 
not a valid objc class.

You have to either:
1) inherit from a valid root class (NSObject).
2) add a "Class isa" ivar to your declaration.

See the NSObject declaration:

@interface NSObject <NSObject> {
    Class    isa;
}
...
@end