Re: [Pyobjc-dev] Mixin classes

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

On 8 May, 2009, at 1:46, Greg Ewing wrote:

> Ronald Oussoren wrote:
>
>> Mixins cannot be used to add new  methods that the ObjC runtime  
>> will see.
>
> In PyGUI I'm using the following metaclass to get a
> similar effect to multiple inheritance. It merges the
> class dicts of all the base classes before creating
> the class.
>
> Usage example:
>
> class PyGUI_NSWindow(NSWindow, PyGUI_NS_EventHandler):	
>  __metaclass__ = NSMultiClass
>  ...
>
> The first base class should be an ObjC class; the
> rest can be ordinary Python classes.
>
> Note that this implementation results in methods in
> later base classes overriding those in earlier ones,
> which is more or less the opposite of what normally
> happens. If you use this technique, you might want
> to reverse the order of the merging.

Wouldn't it be more useful to tweak NSMulticlass to do the updates of  
the class dict in the right order?

Ronald

>
> #--------------------------------------------------
>
> from inspect import getmro
>
> def NSMultiClass(name, bases, dic):
>  #  Workaround for PyObjC classes not supporting
>  #  multiple inheritance properly. Note: MRO is
>  #  right to left across the bases.
>  main = bases[0]
>  dic2 = {}

That is:
      for mix in bases[::-1]:
>  for mix in bases[1:]:
>    for cls in getmro(mix)[::-1]:
>      dic2.update(cls.__dict__)

      # drop the next line:
>  dic2.update(dic)
>  cls = type(main)(name, (main,), dic2)
>  return cls
>
> #--------------------------------------------------
>
> -- 
> Greg