Why isn't the super class of a meta class of a root class a NULL pointer?
class, objective-c, objective-c-runtime
Solution
The Obective-C language specifically decided that class objects should respond to the instance methods of their root class. This is primarily a pragmatic decision; since NSObject is mostly responsible for handling the fundamentals of how ObjC interacts with objects, it would be annoying to have to implement everything twice; once for class objects and once for instances. Class objects can be put into arrays, etc. so they need to respond to `-retain` and `-release` just like instances do.
You can read more about it in the "Methods of the Root Class" section of this document: https://developer.apple.com/library/ios/DOCUMENTATION/Cocoa/Conceptual/ObjectiveC/Chapters/ocObjectsClasses.html
Problem
In the objective-c runtime, a class is represented by a structure like this: ``` typedef struct class_t { struct class_t *isa; // Points to the class' meta class struct class_t *super; // Points to the class' super class Cache cache; IMP *vtable; union { class_ro_t *rodata; class_rw_t *rwdata; }; } class_t; ``` When a `MyClass` class is a root class and not a meta class, its super member is a NULL pointer (which is understandable, since it is a root class, so it doesn't have a super class). However, if we get the isa member of that same `MyClass` root class (which points to `MyClass`' meta class), and we get the super member of that isa member, it is not a NULL pointer, but a pointer to `MyClass` (not meta class). Shouldn't the super class of a meta class of a non-meta root class be a NULL pointer (as the super class of a non-meta root class is)? Since it's not, for what is it supposed not to be? I'm asking this because, the way things are actually, if `methodX` is an instance method (not a class method) of a `MyClass` root class, the statement `[MyClass methodX]` would call `methodX` (and it actually does), what shouldn't happen (again, because `methodX` is a instance method, not a class method, so it should not respond to the `[MyClass methodX]` statement).