We'll start from where we left off in the previous article on [PHP Interfaces](/blog/drupal-8/interface). If you haven't read it, please go and read it now, or get the free eBook on object-oriented programming from the right sidebar (below the content if you are viewing in mobile). In previous article on PHP Interfaces, we made `HondaAccord` class implement the `ContainerInterface` because it has a trunk. As a result, we could use `HondaAccord` class wherever `ContainerInterface` is used. But the code looks ugly!