NSOrderedSet KVO Collection Operators tests

orderedset-kvo-test.m

//
// clang orderedset-kvo-test.m -framework Foundation && ./a.out
//

#import <Foundation/Foundation.h>
#import <objc/runtime.h>
#import <objc/message.h>

int main ()
{
    @autoreleasepool {

        
        id collection = [NSOrderedSet orderedSetWithArray:
                         @[
                         @{@"values": @[@1, @2]},
                         @{@"values": @[@3, @4]},
                         @{@"values": @[@1, @3]},
                         ]
                         ];
        @try {
            NSLog(@"union : %@",[collection valueForKeyPath:@"@distinctUnionOfArrays.values"]);
        } @catch (id e) { NSLog(@"crash : %@",e); }

        /*
         
         Dynamically add this method :
         
         @implementation NSOrderedSet
         - (id) _distinctUnionOfArraysForKeyPath:(NSString*) keyPath
         {
	         return [[self array] _distinctUnionOfArraysForKeyPath:keyPath];
         }
         @end
         
         */

        SEL selector = @selector(_distinctUnionOfArraysForKeyPath:);
        class_addMethod([NSOrderedSet class],
                        selector,
                        imp_implementationWithBlock(^ (id self, NSString* keyPath)
                                                    {
                                                        return objc_msgSend([self array], selector, keyPath);
                                                    }),
                        method_getTypeEncoding(class_getInstanceMethod([NSArray class],selector)));
        
        // This works now !
        NSLog(@"union : %@",[collection valueForKeyPath:@"@distinctUnionOfArrays.values"]);
        
    }
    return 0;
}

output.log

> clang orderedset-kvo-test.m -framework Foundation && ./a.out && rm a.out
2012-11-22 18:25:03.035 a.out[67891:707] crash : [<__NSOrderedSetI 0x7f8050c0d0d0> valueForKeyPath:]: this class does not implement the distinctUnionOfArrays operation.
2012-11-22 18:25:03.037 a.out[67891:707] union : (
    3,
    2,
    1,
    4
)

What about implementing private methods?

@implementation NSOrderedSet (MyKeyValueCoding)

- (id)_distinctUnionOfArraysForKeyPath:(NSString *)keyPath
{
    return [[self array] valueForKeyPath:[NSString stringWithFormat:@"@distinctUnionOfArrays.%@", keyPath]];
}

@end

The problem with @array.@distinctUnionOfArrays.values is that KVC detects the period after @array and then try to use it as a collection operation (which is not implemented) before looking for the existence of the array method.