Re: [Pyobjc-dev] DictType -> ObjC

[Bill B. <bb...@co...>]

On Thursday, October 17, 2002, at 04:32 PM, Jack Jansen wrote:
> On donderdag, oktober 17, 2002, at 01:12 , Bill Bumgarner wrote:
>>     How hard would it be to proxy DictType, ArrayType, and TupleType 
>> into Obj-C such that they look/feel/act/behave/are subclasses of 
>> NSDictionary and NSArray?
>>
>>     That is, such that they implement the primitive methods of the 
>> NSDictionary/NSArray class clusters and internally use the Py* APIs 
>> to retrieve/set values [converting as necessary]?
>>
>>     This would be significantly valuable in that it doesn't imply a 
>> conversion as the objects come across the bridge from Python->ObjC, 
>> yet they would be compatible with NSDictionary/NSArray and friends.
>
> Will these objects still be compatible with CoreFoundation? I'm not 
> familiar enough with how Apple made CF and NS objects interchangeable, 
> but if Pyobjc would handle most objects not by actually converting 
> them but by putting them in something that merely 
> "looks/feels/acts/behaves" like the real NS class that may not be good 
> enough. I assume that "are" is good enough, but again I'm not sure.

Yes -- it is simply a matter of implementing the appropriate primitive 
methods for each class [for class clusters]:

#import <Foundation/Foundation.h>
#import <CoreFoundation/CoreFoundation.h>

@interface FooArray:NSArray
id stuff[100];
@end
@implementation FooArray
- init
{
   [super init];
   int i;
   for(i = 0; i < 100; i++) stuff[i] = [[NSNumber numberWithInt: i] 
retain];
   return self;
}
- (id) objectAtIndex: (int) anIndex { return stuff[anIndex]; }
- (unsigned) count { return 100; }
@end

int main (int argc, const char * argv[]) {
   NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
   FooArray *fooArray = [[FooArray alloc] init];
   NSLog(@"objectAtIndex: 76 -- %@ - 0x%x",
		    [fooArray objectAtIndex: 76],
		    [fooArray objectAtIndex: 76]);
   CFArrayRef fooRef = (CFArrayRef) fooArray;
   NSLog(@"CFArrayGetValueAtIndex(..., 76) -- %@ - 0x%x",
		    CFArrayGetValueAtIndex(fooRef, 76),
		    CFArrayGetValueAtIndex(fooRef, 76));
   [pool release];
   return 0;
}

Outputs:

2002-10-17 16:54:06.121 arraytest[23625] objectAtIndex: 76 -- 76 - 
0x59a80
2002-10-17 16:54:06.122 arraytest[23625] CFArrayGetValueAtIndex(..., 
76) -- 76 - 0x59a80

The same can generally be said/done with any no-cost bridged object, 
just that it may require more methods to be implemented.

In any case, a PyArray subclass simply has to provide implementations 
of -objectAtIndex: and -count:.  All other methods in the NSArray API 
are implemented against those two primitive methods.   The CF "no cost" 
bridge is truly a "no cost" bridge -- it just calls the method IMPs 
directly (not sure how it looks 'em up).

The source to the CF<->NS 'no cost' bridge is in the Darwin CVS 
repository -- CFBase, I believe.

b.bum