In this chapter, we discussed how to define custom data types—structures and classes. Then, we defined some custom types in our playground to see this in practice. You should be able to define your own data types. We've learned what is subclassing and inheritance. You now know how to override methods and properties. We explored the very popular design pattern, MVC. If you organize the app following the MVC pattern, then some parts of our apps can be reused in other apps without further improvements. They will be designed for future reuse.
In the next chapter, we will add interactivity to our first application. We will try to apply the MVC in practice in our mobile app. Let's get started with storyboards and views, then we will add some buttons and hook up some actions to those buttons.