@interface DKRuntimeHelper : NSObject
  + (NSArray*) allClasses;
  + (NSArray*) allClassesOfKind:(Class) aClass;
@end

@implementation DKRuntimeHelper
 
  + (NSArray*) allClasses {
    return [self allClassesOfKind:[NSObject class]];
  }
 
  + (NSArray*) allClassesOfKind:(Class) aClass {
    // returns a list of all Class objects that are of kind <aClass> or a subclass of it currently
    // registered in the runtime. This caches the result so that the relatively expensive
    // run-through is only performed the first time
    static NSMutableDictionary* cache = nil;
 
    if ( cache == nil )
      cache = [[NSMutableDictionary alloc] init];
 
    // is the list already cached?
    NSArray* cachedList = [cache objectForKey:NSStringFromClass( aClass )];
 
    if ( cachedList != nil )
      return cachedList;
 
    // if here, list wasn't in the cache, so build it the hard way
    NSMutableArray* list = [NSMutableArray array];
 
    Class* buffer = NULL;
    Class  cl;
 
    int i, numClasses = objc_getClassList( NULL, 0 );
 
    if( numClasses > 0 )  {
      buffer = malloc( sizeof(Class) * numClasses );
      NSAssert( buffer != nil, @"couldn't allocate the buffer");
      (void) objc_getClassList( buffer, numClasses );
 
      // Go through the list and carefully check whether the class can respond to isSubclassOfClass:
      // If so, add it to the list.
 
      for( i = 0; i < numClasses; ++i ) {
        cl = buffer[i];
        if( classIsSubclassOfClass( cl, aClass ))
          [list addObject:cl];
      }
      free( buffer );
    }
 
    // save in cache for next time
    [cache setObject:list forKey:NSStringFromClass( aClass )];
 
    return list;
  }
 
@end

BOOL classIsNSObject( const Class aClass ) {
  // returns YES if <aClass> is an NSObject derivative, otherwise NO.
  // It does this without invoking any methods on the class being tested.
  return classIsSubclassOfClass( aClass, [NSObject class]);
}
 
BOOL classIsSubclassOfClass( const Class aClass, const Class subclass ) {
  Class temp = aClass;
  int match = -1;
 
  while((match = strncmp(temp->name, subclass->name, strlen(subclass->name))) && (temp->super_class != NULL))
    temp = temp->super_class;
 
  return ( match == 0 );
}