gistfile1.m

- (void)setCallbackBlock:(void (^)(id object))callbackBlock
{
  //set block as an attribute in runtime
  if (callbackBlock) {
    objc_setAssociatedObject(self, "dismissBlockCallback", [callbackBlock copy], OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    return;
  }
  
  void (^block)(id obj) = objc_getAssociatedObject(self, "dismissBlockCallback");
  if (block)
    objc_removeAssociatedObjects(block);
}

//Return YES if there is a block object
- (BOOL)performCallbackBlockWithObject:(id)object
{
  //get back the block object attribute we set earlier
  void (^block)(id obj) = objc_getAssociatedObject(self, "dismissBlockCallback");
  if (block) {
    block(object);
    return YES;
  }
  
  return NO;
}

Simple Swift conversion attempt:

var dismissBlockCallback : (obj: AnyObject) -> (Void)!

func setCallbackBlock(callbackBlock: (object: AnyObject) -> (Void)) {
    if callbackBlock { // Type '(object: AnyObject) -> (Void)' does not conform to protocol 'LogicValue'
        self.dismissBlockCallback = callbackBlock
    }
    else {
        self.dismissBlockCallback = nil
    }
}

func performCallbackBlockWithObject(object: AnyObject) -> Bool {
    if self.dismissBlockCallback { // '(obj: AnyObject) -> (Void)!' does not conform to protocol 'LogicValue'
        self.dismissBlockCallback(object)
        return true;
    }

    return false;
}

Take 2

var dismissBlockCallback : ((obj: AnyObject) -> Void)?

func setCallbackBlock(callbackBlock: ((object: AnyObject) -> Void)?) {
    if callbackBlock {
        self.dismissBlockCallback = callbackBlock
    }
}

func performCallbackBlockWithObject(object: AnyObject) -> Bool {
    if self.dismissBlockCallback {
        self.dismissBlockCallback!(obj: object)
        return true
    }
    return false
}