In previous chapters, we briefly touched on the map function as an example of a built-in higher-order function. In this chapter, we will explore this topic further and get familiar with the map, flatMap, filter, and reduce functions in Swift, together with examples. We will also get familiar with the category/type theory concepts such as higher-kinded types (Monad, Functor, and Applicative Functor).
This chapter will cover the following topics with coding examples:
- Functors
- Applicative Functors
- Monads
- The map function
- The flatMap method
- The filter function
- The reduce function
- The apply function
- The join function
- Chaining higher-order functions
- The zip function
- Practical examples
Collections are used everywhere in our day-to-day development, and to be able to use collections declaratively, we need means such as map, filter, and reduce. Before going through these functions that are built into Swift, let's explore the theoretical background of these concepts.