NSObject+AssociatedDictionary

NSObject+AssociatedDictionary.h

#import <Foundation/Foundation.h>

@interface NSObject (AssociatedDictionary)

+ (NSMutableDictionary*)associatedDictionary;
- (NSMutableDictionary*)associatedDictionary;

@end

NSObject+AssociatedDictionary.m

#import "NSObject+AssociatedDictionary.h"
#import <objc/runtime.h>

@implementation NSObject (AssociatedDictionary)

static NSDictionary* associatedDictionary(id object, const void* key)
{
    NSMutableDictionary* dict = objc_getAssociatedObject(object, key);
    if (!dict) {
        dict = [NSMutableDictionary dictionaryWithCapacity:1];
        objc_setAssociatedObject(object, key, dict, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
    return dict;
}

+ (NSDictionary*)associatedDictionary
{
    const void* key = (__bridge const void *)(self);
    return associatedDictionary(self, key);
}

- (NSDictionary*)associatedDictionary
{
    const void* key = @selector(associatedDictionary);
    return associatedDictionary(self, key);
}

@end