You don't actually need the @interface section.

Using class-dump on CoreFoundation, I see NSObject implements all of these:

- (BOOL)isNSArray__;
- (BOOL)isNSData__;
- (BOOL)isNSDate__;
- (BOOL)isNSDictionary__;
- (BOOL)isNSNumber__;
- (BOOL)isNSOrderedSet__;
- (BOOL)isNSSet__;
- (BOOL)isNSString__;
- (BOOL)isNSTimeZone__;
- (BOOL)isNSValue__;

May want to implement all of them if going this route.