Question

We know that in Objective-C there are two main root classes: NSObject and NSProxy. There are other roots (mainly for private and legacy purposes) like Object, and NSLeafProxy.

Defining a new root is fairly trivial:

@interface DDRoot <NSObject>

@end

@implementation DDRoot

//implement the methods required by <NSObject>

@end

My question is: why would you ever want to define a new root class? Is there some use-case where it’s necessary?

Answer 1

As far as I can tell, there should be no reason for creating your own root class, because short of implementing all of the NSObject protocol methods yourself, you’re going to be missing out on a lot of functionality, and going to be making a lot of calls to the Objective-C runtime that should essentially be done for you.

Unless you really had to implement the protocol differently from the default (NSProxy is a special case that does have to), you shouldn’t need to make your own root class. I mean, you’d have to be writing a class that cannot fundamentally be represented by NSObject and the protocol as implemented by Apple, and in that case, why are you even writing it in Objective-C?

That’s what I think. Maybe someone can come up for a creative use for it.

(People researching the topic should go look at the NSObject Class Reference, NSObject Protocol Reference, ‘Core Competencies: Root Class’ document, and the ‘Root Class’ section of the Fundamentals Guide: Cocoa Objects document.)