In this chapter, we covered the Scala Collection library. We covered how to work with lists, which will make us familiar with some design principles of the whole collections library. We also covered how to generalize to sequences and covered some more relevant data structures. Finally, we also covered how collections relate to monads and how we can use that knowledge to use some powerful abstractions in our code.

In the next chapter, we will cover the type system and polymorphism. We will also cover the different types of variance, which provides a way to constrain parameterized types. Finally, we will cover some advanced types like abstract type members, option, and so on.