Re: Use of 'count' in KVC for NSArray and NSDictionary

[Helge Hess]

On 13. Mrz 2006, at 14:54 Uhr, Richard Frith-Macdonald wrote:
> I believe the behavior of Key Value Coding in MacOS-X has changed  
> compared to the behavior currently implemented in the GNUstep base  
> library for classes like NSArray and NSDictionary.  Is there any  
> reason why we should not change to maintain/regain compatibility?
> The old behavior was to return the count of objects in the  
> collection, but the new behavior seems to be to return an array  
> containing the results of calling -valueForKey:@"count" on all the  
> objects.

To elaborate this a bit further ...

In current Cocoa (10.4) NSArray and NSDictionary are very specific  
about special KVC keys in those two classes.
The rule is simple: if the key starts with an @ (like @count, @max  
etc), [super valueForKey:] is used to resolve the key instead of  
doing the collection specific processing (which is performing  
valueForKey: on the elements for NSArray and using -objectForKey: for  
NSDictionary).

I *think* this @ rule was always implemented that way in NeXT/Apple  
stuff (even in early EOF which introduced KVC). And that the GNUstep  
special keys are an incompatible, GNUstep specific addition (probably  
someone added that to have a way to access the count of the array but  
didn't know about the @ stuff).
But I'm not perfectly sure (only 97%).

Gstep-base currently has hacks for special keys w/o the @ prefix and  
is therefore incompatible with Cocoa.

Greets,
  Helge

PS: actually the @ rule is documented in the Apple docs of  
NSDictionary but not in NSArray. But the implementation is the same  
on 10.4, I checked this.
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