gistfile1.txt

@interface _KeyPathObserver : NSObject
@end

@implementation NSObject (Additions)

- (void)performSelector:(SEL)aSelector forChangesInKeyPath:(NSString *)aKeyPath
{
    [self addObserver:(id)[_KeyPathObserver class] forKeyPath:aKeyPath options:NSKeyValueObservingOptionNew context:aSelector];
}

@end

@implementation _KeyPathObserver

+ (void)observeValueForKeyPath:(NSString *)aKeyPath ofObject:(id)anObject change:(NSDictionary *)aChange context:(void *)aContext
{
    [anObject performSelector:(SEL)aContext];
}

@end