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

[Bob I. <bo...@re...>]

On Nov 5, 2003, at 5:00 AM, Ronald Oussoren wrote:

> 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)'.

Well the current semantics for instance method only and class method 
only are perfectly fine.. it's the occasions when a particular selector 
is implemented both ways where things start to get hairy.  I'd rather 
have NSObject.description(obj) not work, if it meant that 
NSObject.description() did work.  Even still, I think enough 
information is available to make it possible.  What about something 
like this (sorta pseudocode, not in tp_descr_get C API).

METH_CLASS = 1 << 0
METH_INST  = 1 << 1

class Selector(object):
     EXPECTED_ARG_LEN = 0
     def __init__(self, name, flags, boundklass=None, boundinst=None):
         self.name = name
         self.flags = flags
         self.boundklass = boundklass
         self.boundinst = boundinst

     def __get__(self, inst, klass):
         if inst is None:
             return Selector(self.name, self.flags, boundklass=klass)
         elif not (self.flags & METH_INST):
             # trying to get a pure class method from an instance, don't 
do that
             raise AttributeError, "%s is a class method" % (self.name,)
         # it's been acquired from an instance
         return Selector(self.name, self.flags, boundinst=inst, 
boundklass=klass)

     def __call__(self, *args):
         if self.boundklass is None and self.boundinst is None:
             raise ValueError, "Selector not initialized"
         elif self.boundinst is not None:
             # acquired from an instance..
             return execute(self.boundinst, args)
         elif self.flags & METH_INST and len(args) > 
self.EXPECTED_ARG_LEN:
             # must be using class.instanceMethod(instance, ....)
             # so what if this breaks down on varargs? how are varargs 
wrapped anyway (if at all)?
             # those people can use a workaround or just not use 
klass.instanceMethod(instance, ...)
             return execute(args[0], args[1:])
         else:
             return execute(self.boundklass, args)