Building Dynamic Classes in Objective C

Posted by kjell_ on Stack Overflow See other posts from Stack Overflow or by kjell_
Published on 2010-03-15T13:41:38Z Indexed on 2010/03/15 13:49 UTC
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I'm a somewhat competent ruby programmer. Yesterday I decided to finally try my hand with Apple's Cocoa frameworks. Help me see things the ObjC way?

I'm trying to get my head around objc_allocateClassPair and objc_registerClassPair. My goal is to dynamically generate a few classes and then be able to use them as I would any other class. Does this work in Obj C?

Having allocated and registered class A, I get a compile error when calling [[A alloc] init]; (it says 'A' Undeclared). I can only instantiate A using runtime's objc_getClass method. Is there any way to tell the compiler about A and pass it messages like I would NSString? A compiler flag or something?

I have 10 or so other classes (B, C, …), all with the same superclass. I want to message them directly in code ([A classMethod], [B classMethod], …) without needing objc_getClass. Am I trying to be too dynamic here or just botching my implementation? It looks something like this…

 NSString *name = @"test";  
 Class newClass = objc_allocateClassPair([NSString class], [name UTF8String], 0);  
 objc_registerClassPair(newClass);  

 id a = [[objc_getClass("A") alloc] init];  
 NSLog(@"new class: %@ superclass: %@", a, [a superclass]);  
 //[[A alloc] init]; blows up.

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