Using closures as parameters when they accept parameters

This is where closures can start to be read a bit like line noise: a closure you pass into a function can also accept its own parameters.

We’ve been using () -> Void to mean “accepts no parameters and returns nothing”, but you can go ahead and fill the () with the types of any parameters that your closure should accept.

To demonstrate this, we can write a travel() function that accepts a closure as its only parameter, and that closure in turn accepts a string:

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

Now when we call travel() using trailing closure syntax, our closure code is required to accept a string:

travel { (place: String) in
    print("I'm going to \(place) in my car")
}

SPONSORED ViRE offers discoverable way of working with regex. It provides really readable regex experience, code complete & cheat sheet, unit tests, powerful replace system, step-by-step search & replace, regex visual scheme, regex history & playground. ViRE is available on Mac & iPad.

Download on the App Store

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