Re: [Pyobjc-dev] Mixin classes

[Greg E. <gre...@ca...>]

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.

#--------------------------------------------------

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 = {}
   for mix in bases[1:]:
     for cls in getmro(mix)[::-1]:
       dic2.update(cls.__dict__)
   dic2.update(dic)
   cls = type(main)(name, (main,), dic2)
   return cls

#--------------------------------------------------

-- 
Greg