Objective-C introspection methods

ObjCIntrospect.h

#import <Foundation/Foundation.h>
 
 
/** ClassGetSubclasses
 
 Returns all subclasses for a given class by interrogating every class in the 
 runtime. Results are cached to save time on repeat calls for the same class.
*/
extern NSArray *ClassGetSubclasses(Class parentClass);

ObjCIntrospect.m

#import "ObjCIntrospect.h"
 
#import <objc/runtime.h>
 
 
static NSMutableDictionary *ClassSubclassesCache;
 
 
NSArray *ClassGetSubclasses(Class class) {
    
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        ClassSubclassesCache = [NSMutableDictionary dictionary];
    });
    
    NSMutableArray *result = [ClassSubclassesCache objectForKey:NSStringFromClass(class)];
    
    if (result == nil) {
        
        int numClasses = objc_getClassList(NULL, 0);
        Class *classes = NULL;
        
        classes = malloc(sizeof(Class) * numClasses);
        numClasses = objc_getClassList(classes, numClasses);
        
        for (NSInteger i = 0; i < numClasses; i++) {
            
            Class superClass = classes[i];
            
            do {
                superClass = class_getSuperclass(superClass);
            } while(superClass && superClass != class);
            
            if (superClass == nil) {
                continue;
            }
            
            [result addObject:classes[i]];
        }
        
        free(classes);
        
        [ClassSubclassesCache setObject:result forKey:NSStringFromClass(class)];
    }
    
    return result;
}