[Pyobjc-dev] Bridging of Strings

[<bb...@ma...>]

On Sunday, Dec 22, 2002, at 18:20 US/Eastern, David Eppstein wrote:
> Shouldn't this work?
>
> NSString.localizedCaseInsensitiveCompare_('foo','bar')
>
> When I try it I get a complaint that the argument should be an  
> NSString instead of a Python string.  I guess this means there is a  
> signature missing somewhere?  I don't understand signatures well  
> enough to correct it.
>
>
> Really it would be better to be able to call
> 'foo'.localizedCaseInsensitiveCompare_('bar')
> but I can see why that's unlikely to work...

That is exactly what you *should* be able to call but for another  
problem.  Actually, either form should work in the Python sense.

This is sort of a bug in the bridge and a feature.

Bug:

This....

     NSString.localizedCaseInsensitiveCompare_('foo', 'bar')

     ... should really work, but complains about "First argument must be  
an objective-C object, got 'foo'".   I'm somewhat surprised that the  
bridge doesn't convert 'foo' to an NSString as it hits the bridge  
because it is a feature of the bridge to transparently convert Strings  
to their native ObjC/Python type as they pass across the bridge.

     Rethinking this, the above method call may not work in some  
situations.  In particular, in class clusters it is often the case that  
you generally interact with some private subclass.  For example,  
NSArray.count(someArray) will not actually do what you want because  
instances of NSArray are never directly instantiated-- just private  
subclasses.

In [6]: a = NSArray.arrayWithArray_([1,2,3,4,5])
In [7]: a.count()
Out[7]: 5
In [8]: NSArray.count(a)
------------------------------------------------------------------------ 
---
ValueError                                Traceback (most recent call  
last)

?

ValueError: NSInvalidArgumentException - *** -count only defined for  
abstract class.  Define -[NSCFArray count]!

---

     So-- given that we can't call the methods on NSString via the class  
object, we really need to be able to pass an NSString across the bridge  
such that it remains an NSString on the Python side.   There are a  
number of reasons for this-- not duplicating data and having access to  
the localization methods being the primary reasons.

     A workaround (for David and others, not a recommendation for a  
possible solution in the bridge):

     Create an NSBundle that contains a category or class that wraps the  
methods on NSString that you need access to.  I.e....

@implementation NSString (BridgedMethods)
+ (NSComparisonResult)string: (NSString *) aString  
localizedCaseInsensitiveCompare:(NSString *)bString;
{
     return [aString localizedCaseInsensitiveCompare: bString];
}
@end

... to be invoked [after loading] as ...

     NSString.string_localizedCaseInsensitiveCompare_('foo', 'bar')

... not as elegant as an instance method and not directly compatible  
with the various sorting methods on Array and the like.

     b.bum