NSProxy

class.h

@interface AAA : NSProxy

@property (nonatomic, weak) id target;
- (instancetype)initWithTarget:(id)target;
+ (instancetype)proxyWithTarget:(id)target;

@end

class.m

@implementation AAA

- (instancetype)initWithTarget:(id)target{
  _target = target;
  return self;
}

+ (instancetype)proxyWithTarget:(id)target{
  return [[self alloc] initWithTarget:target];
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel{
  return [self.target methodSignatureForSelector:sel];
}

- (void)forwardInvocation:(NSInvocation *)invocation{
  SEL sel = [invocation selector];
  if ([self.target respondsToSelector:sel]) {
    [invocation invokeWithTarget:self.target];
  }
}

- (BOOL)respondsToSelector:(SEL)aSelector{
  return [self.target respondsToSelector:aSelector];
}

@end