Re: [Pyobjc-dev] Mixin classes

[Ronald O. <ron...@ma...>]

Johan,


On 5 May, 2009, at 16:37, Johan Rydberg wrote:

> I'm trying to implement the informal NSKeyValueBindingCreation  
> protocol.
> I would love to make it a mixin-class so I can reuse the functionality
> throughout
> my application.
>
> Here's how I planned to do it:
>
> class NSKeyValueBindingCreation:
>   def bind_toObject_withKeyPath_options_(self, binding, anObject,
> keyPath, options):
>       ...
>   def observeValueForKeyPath_ofObject_change_context_(self, keyPath,  
> anObject,
>                                                        change,  
> context):
>       ....
>
> class Foo(NSObject, NSKeyValueBindingCreation):
>   ....
>
> The problem is that my Foo class won't recognize the
> observiceValueForKeyPath:ofObject:change:context: message.
>
> objc.error: NSInternalInconsistencyException - <Foo: 0x35e430>: An
> -observeValueForKeyPath:ofObject:change:context: message was received
> but not handled.
>
>
> If I put it directly in Foo it gets recognized.
>
> Poking through the PyObjC manual I found the following lines:
>
> Multiple inheritance may be used when subclassing an Objective-C
> class, so long as the Objective-C class is the first base class and  
> there
> is only one Objective-C base class. The Objective-C runtime does not
> support multiple inheritance. These mix-in classes should not contain
> different implementations for Objective-C methods. To achieve this
> behavior, Categories should be used instead.
>
> I interpret those lines as that the snippets above should work.
> Am I wrong?

Yes ;-)

>
> How can I, and how should I use mixin classes?

You cannot do this at the moment. Mixins cannot be used to add new  
methods that the ObjC runtime will see.

I might add this behaviour in the future, I like your usecase and this  
could be used to make useful common functionality available as mixin  
classes.    Adding this will require a detailed specification and  
testsuite, the objc runtime doesn't support multiple-inheritance  
itself and hence support for mixin classes will require some tricks.

I'm especially worried about getting the semantics exactly like they'd  
be if the base-class is a regular Python class.

Ronald
>
> ------------------------------------------------------------------------------
> The NEW KODAK i700 Series Scanners deliver under ANY circumstances!  
> Your
> production scanning environment may not be a perfect world - but  
> thanks to
> Kodak, there's a perfect scanner to get the job done! With the NEW  
> KODAK i700
> Series Scanner you'll get full speed at 300 dpi even with all image
> processing features enabled. http://p.sf.net/sfu/kodak-com
> _______________________________________________
> Pyobjc-dev mailing list
> Pyo...@li...
> https://lists.sourceforge.net/lists/listinfo/pyobjc-dev