Swift Programming: The Big Nerd Ranch Guide

Functions as Return Types

Now that you have more experience with functions and closures, recall from Chapter 12 that every function has a function type. A function type defines a function’s or closure’s parameter and return types. For example, a function that takes a String argument and returns an Int has the function type of (String) -> Int. Function types are frequently used to determine what sort of closure you need to satisfy a given parameter’s type or what sort of function needs to be returned.

In Swift, functions are first-class objects. One implication of this is that functions can return other functions as their return type. Remember your little town of Knowhere? It is time to make a function to improve your town. You are ...