Re: [Pyobjc-dev] [ pyobjc-Bugs-836247 ] NSWindow.contentRectForFrameRect_styleMask_ not a class meth

[Ronald O. <ous...@ci...>]

Managment summary:

use 'NSWindow.pyobjc_classMethods.contentRectForFrameRect_styleMask_'  
to call the class method.

On 5 nov 2003, at 9:23, Bob Ippolito wrote:

> On Nov 4, 2003, at 10:56 PM, SourceForge.net wrote:
>
>> Bugs item #836247, was opened at 2003-11-05 03:56
>> Message generated for change (Tracker Item Submitted) made by Item  
>> Submitter
>> You can respond by visiting:
>> https://sourceforge.net/tracker/? 
>> func=detail&atid=114534&aid=836247&group_id=14534
>
> This bug exposes a fairly obnoxious problem in the current  
> implementation of PyObjC: there are not separate namespaces for class  
> and instance methods, so you end up with stupid problems when you have  
> some class that implements the same selector for both the instance and  
> class.  There's a lot of pretty common selectors that are like this:
> 	+[NSObject description]
> 	-[NSObject description]
> 	.. etc ..

I noticed. It is already possible to call both methods, although not  
necessarily in a very convenient way:

	NSObject.foo()		# Instancemethod, or if that does not exist classmethod
	NSObject.pyobjc_classMethods.foo()	# Classmethod
	NSObject.pyobjc_instanceMethods.foo()	# Instancemethod

At the time we ran into this issue I couldn't find any methods where it  
would be usefull to override the class method, it is therefore not  
possible to override the class method at the moment.

>
> I did discover a workaround, which is  
> ClassObject.bothClassAndInstanceMethod(ClassObject).. for example:
> >>> NSObject.description(NSObject)
> u'<NSObject: 0xa0a04e40>'

That's more a bug than a feature...

>
> Ideally one would be able to do NSObject.description().. which means  
> that the descriptor has to know about these "class or instance"  
> methods.  It's also, as far as I know, not possible to override the  
> class implementation for a selector if an instance implementation  
> exists (from Python).

Note that it is currently not possible to know of  
'NSObject.description' refers to the class or instance method due to  
the way types are implemented in Python:

	obj.description()

is basically implemented as:
	
	obj.__class__.description(obj)

And furthermore Cocoa classes should 'feel' as much as Python classes  
as possible, it should therefore be possible to call  
'NSObject.description(obj)'.

>
> So my question is, how the heck do we approach this?  It seems that  
> the current selector objects/descriptors need to be changed quite a  
> bit in order to facilitate this, especially allowing one to do it from  
> Python.  Perhaps we can change the selector function to take a class  
> function, instance function, or both.. and throw away isClassMethod.   
> We can add a flag on the selector that says "I have both a class and  
> an instance".  I'm pretty new to these internals.. so, Ronald, do you  
> want to handle this one?  Or give me some ideas as to how this should  
> be done?

Is it necessary to be able to override class methods? My gut feeling is  
that it would be easy-ish to change objc.selector() to allow something  
like this:

	class FooClass (NSObject):
		def _cls_description(cls):
			return "FooClass class"

		def _inst_description(self):
			return "FooClass instance"

		description = objc.selector(selector="description",  
clsImp=_cls_description, instImp=_inst_description)

		del _cls_description, _inst_description

This is pretty ugly, but at least would make it possible to override  
both the class and instance method without introducing an additional  
class.

However, I don't think this is worth the effort unless someone has a  
real use case. 	

Ronald