In the previous chapter, you learned how functional programming and metaprogramming make it possible to customize the behavior of functions. We can create a function within a certain context, which is called a closure. We can also use higher order functions by passing functions around just like other objects.
In this chapter, you will learn how to customize the behavior of objects by walking into the world of object-oriented programming. R provides several different object-oriented systems to work with. At first glance, they look quite different from the object-oriented systems in other programming languages. However, the idea is mostly the same. I will briefly explain the concept of class and method of objects, and show you how they can be useful in unifying the way we work with data and models.
We will cover the following topics at the beginner level in the subsequent sections:
The idea of object-oriented programming
S3 system
S4 system
Reference class...
