Re: Why is +initialize not inherited?

[Larry Campbell]

On Jan 21, 2006, at 4:50 AM, David Ayers wrote:

> Larry Campbell schrieb:
> > In Apple's runtime +initialize is inherited (and this is  
> > documented,  so
> > it's not by accident). In gnustep it's not. Is there a good  
> > reason  for
> > this? It seems like a glaring inconsistency -- "subclasses  inherit
> > methods from their superclass _unless_ the method is called
> > +initialize". Seems to me it would be much cleaner to not special-  
> > case
> > this and for +initialize to be inherited.
>
> Have a look at this discussion:
>
> http://lists.apple.com/archives/objc-language/2004/Mar/msg00006.html
>
> Now, I'm no advocate of being different just for the sake of being
> different, but I also think that '+load' and '+initialize' are simply
> "special" wrt inheritance and guarantees on how/when they are  
> called and
> I would assume that we would break code written for the FSF libobjc
> runtime if FSF's libobjc started to inherit +initialize.

However, I think that:

1. The difference between FSF here and Apple is a trap for the unwary
2. It would be best to remove such traps when possible
3. Due to binary compatibility it's extremely unlikely Apple will change
4. There's no clear advantage to the FSF approach (or the Apple  
approach)
5. If you really want to share initialization code with subclasses,  
you have to move such initialization code into a separate method, or  
subclasses have to call [super initialize]

So I think I would argue that FSF should consider changing; not  
precipitously, and with perhaps a way to override via an environment  
variable in case of compatibility bugs.

> Note that if you actually invoked either +initialize or +load in a  
> true
> method invocation, the normal inheritance techniques would be  
> used.  But
> be warned, code often is not prepared for multiple invocations of  
> these
> methods and could break in strange ways (e.g. replacing objects/caches
> which were meant to be initialized as singletons).

Yes, sadly all my initialize methods now have to look like this:

+ (void)initialize
{
    if (self == [MyClass class]) {
        static BOOL inited = NO;
        if (!inited) {
            // do stuff
        }
    }
}

(This still doesn't help with category initialize, but I try to avoid  
categories and I've never tried category initialize)

- lc