More KVC weirdness with NSOrderedSets

orderedsets-more-kvc.m

//
// clang orderedsets-more-kvc.m -framework Foundation && ./a.out
//

#import <Foundation/Foundation.h>

int main ()
{
    @autoreleasepool {

        id data = (@[
                   @{ @"values": [NSOrderedSet orderedSetWithArray:@[@1, @2, @3, @4]] },
                   @{ @"values": [NSOrderedSet orderedSetWithArray:@[@1, @3, @5, @7]] }
                   ]);

        // valueForKeyPath logs an error, but somehow manages to return the correct result.
        NSLog(@"union : %@",[data valueForKeyPath:@"@distinctUnionOfArrays.values"]);
        /*
         2012-11-23 09:34:47.507 a.out[12956:707] *** -[NSMutableArray addObjectsFromArray:]: array argument is not an NSArray
         2012-11-23 09:34:47.509 a.out[12956:707] *** -[NSMutableArray addObjectsFromArray:]: array argument is not an NSArray
         2012-11-23 09:34:47.509 a.out[12956:707] union : (
         5,
         1,
         2,
         7,
         3,
         4
         )
         */

        // Convert each OrderedSet to an Array to mute the error.
        NSLog(@"union : %@",[data valueForKeyPath:@"@distinctUnionOfArrays.values.@array"]);
        /*
         2012-11-23 09:34:41.930 a.out[12927:707] union : (
         5,
         1,
         2,
         7,
         3,
         4
         )
         */
    }
    return 0;
}

Do you have any idea where this @array operator comes from or why it needs to be in the last position? I can't find any mention of such an operator; there's the array property on NSOrderedSet, but that doesn't work as part of the path without the @. Very strange.

If you have a Stack Overflow account and any insight into this issue, please have a look at http://stackoverflow.com/questions/31780983/extracting-properties-from-nsarray-of-nsarray-of-nsdictionary/

Also discovered @set:

[data valueForKeyPath:@"@distinctUnionOfSets.values.@set"]