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 Let’s face it, SwiftUI previews are limited, slow, and painful. Judo takes a different approach to building visually—think Interface Builder for SwiftUI. Build your interface in a completely visual canvas, then drag and drop into your Xcode project and wire up button clicks to custom code. Download the Mac App and start your free trial today!

Try now

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