Closures as parameters

Because closures can be used just like strings and integers, you can pass them into functions. The syntax for this can hurt your brain at first, so we’re going to take it slow.

First, here’s our basic driving() closure again

let driving = {
    print("I'm driving in my car")
}

If we wanted to pass that closure into a function so it can be run inside that function, we would specify the parameter type as () -> Void. That means “accepts no parameters, and returns Void” – Swift’s way of saying “nothing”.

So, we can write a travel() function that accepts different kinds of traveling actions, and prints a message before and after:

func travel(action: () -> Void) {
    print("I'm getting ready to go.")
    action()
    print("I arrived!")
}

We can now call that using our driving closure, like this:

travel(action: driving)

SPONSORED Transform your career with the iOS Lead Essentials. Unlock over 40 hours of expert training, mentorship, and community support to secure your place among the best devs. Click for early access to this limited offer and a FREE crash course.

Click to save your free spot now

Sponsor Hacking with Swift and reach the world's largest Swift community!