Re: Ivars in GUI classes

[Richard Frith-Macdonald]

On 17 Aug 2007, at 03:41, Chris Farber wrote:

> Hello everyone,
>
> I'm beginning to add bindings to the classes listed here:
> http://developer.apple.com/documentation/Cocoa/Reference/ 
> CocoaBindingsRef/index.html#//apple_ref/doc/uid/10000189i
>
> In order to add a binding, a few pieces of information have to be  
> kept track of, such as the value transformer, bound object and key  
> path, and other options. One way to do this would be to add  
> instance variables to the classes, but I am not sure if there would  
> be any negative consequences of this. If you look at the headers on  
> Mac OS X, it appears this is not the route Apple took.  
> Alternatively I could put these in global map tables or  
> dictionaries and use locks to make it thread-safe, but this would  
> be a lot more work (and potentially slower?).
>
> I'd appreciate any advice on which route to take.

I'd use the external map tables rather than instance variables.

Yes, it's a bit more complex (but it avoids clutter in the individual  
class headers) and a bit slower (probably negligible in the context  
of all the other code involved in bindings).

Keeping the info in private external tables means:
The implementation is hidden, so changes can be made between  
different releases of the library without causing binary  
incompatibility.
The code can all be in one place, so it's easier to see it all and  
maintain it.