Re: [Pyobjc-dev] objc classes

[Bob I. <bo...@re...>]

On May 28, 2004, at 4:57 PM, Helge Hess wrote:

> just found that in class-builder.h:
> ---snip---
>  *    Note that it is not possible to remove classes from the 
> Objective-C
>  *    runtime (at least with the Apple runtime, not sure about the GNU 
> runtime).
> ---snap---
>
> I would love to understand what exactly is meant here and how it 
> restricts functionality. Does that only mean that the class structure 
> may not be deallocated and cannot be unlinked?

Yes and yes.

> Is it possible to change the mapping of a class name in the name 
> registry (name to structure) mapping? So that the old class object is 
> still available, but the new class object will be used for new 
> instances?

No and No.

> Further, would it possible to change the class hierarchy of an 
> existing class? So that MyFormatter initially inherits from say 
> NSFormatter and after reloading a Python module inherits from 
> NSDateFormatter. Would that be possible with the Apple ObjC runtime or 
> is this already possible with PyObjC?

No, no, and no.  In fact, you can't even reload the python module.  The 
class can be created once and only once.

 >>> from Foundation import *
 >>> class Foo(NSObject):
...   pass
...
 >>> class Foo(NSObject):
...   pass
...
Traceback (most recent call last):
   File "<stdin>", line 1, in ?
objc.error: Class already exists in Objective-C runtime

Some of the things you ask about are possible though awful hacks, but 
I'm not going to encourage that :)

-bob