Objective C weak associated

Associated.m

- (id)weakObject {
    id (^block)() = objc_getAssociatedObject(self, @selector(weakObject));
    return (block ? block() : nil);
}

- (void)setWeakObject:(id)object {
    id __weak weakObject = object;
    id (^block)() = ^{ return weakObject; };
    objc_setAssociatedObject(self, @selector(weakObject),
                             block, OBJC_ASSOCIATION_COPY);
}