Swift Programming: The Big Nerd Ranch Guide

For the More Curious: Mutating Methods

After working through this chapter, you might be wondering about the mutating keyword. Why is it needed to allow you to modify a struct or enum? A useful place to start is to revisit functions that return functions.

Create a new playground called Mutating. Add a simple function to your playground that returns a String greeting.

Listing 15.16 A simple greeting function

func greet(name: String, withGreeting greeting: String) -> String {
    return "\(greeting) \(name)"
}

The greet(name:withGreeting:) function takes two arguments: a name and a greeting. It constructs and returns a greeting based on these two arguments. This function is straightforward to use.

Listing 15.17 Using greet(name:withGreeting:) ...