Re: [Pyobjc-dev] Categories (was: Subclassing NSTextField)

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

On Tuesday, Dec 17, 2002, at 21:08 Europe/Amsterdam, bb...@ma... wrote:

> On Tuesday, Dec 17, 2002, at 14:25 US/Eastern, Steven D. Arnold wrote:
>
>> On a related note, is there any mechanism to implement categories in 
>> pyobjc?
>> I thought this question had been asked before, but I couldn't find it 
>> in my
>> archive.
>
> Good question:   Ronald?

Not really. You can of course implemenent methods from a category for 
your own subclasses (e.g. like the text* categories Bill mentioned in 
the previous message), but you cannot add new methods to existing 
Objective-C classes. You can add new methods to subclasses defined in 
Python.

Some other useful things you cannot do at the moment (using the 
Internet as my Todo list :-) are:
- Adding new methods to subclassses implemented in Python if those 
methods override/extend existing methods. You can do this, but your 
method won't be called if someone tries to access this method from 
Objective-C.
- Removing methods from subclasses implemented in Python, if those 
methods override/extend existing methods. Again you can actually do 
this, but this doesn't have the right semantics.
- Redefine an existing class. This is a feature: Because Objective-C 
has a flat namespace and python doesn't you might otherwise accidently 
replace and existing class. It is also not really possible to implement 
this without memory leaks.

All of these would be usefull for incremental development and may be 
added in some future version (that includes support for categories).

Ronald