Returning closures from functions

In the same way that you can pass a closure to a function, you can get closures returned from a function too.

The syntax for this is a bit confusing a first, because it uses -> twice: once to specify your function’s return value, and a second time to specify your closure’s return value.

To try this out, we’re going to write a travel() function that accepts no parameters, but returns a closure. The closure that gets returned must be called with a string, and will return nothing.

Here’s how that looks in Swift:

func travel() -> (String) -> Void {
    return {
        print("I'm going to \($0)")
    }
}

We can now call travel() to get back that closure, then call it as a function:

let result = travel()
result("London")

It’s technically allowable – although really not recommended! – to call the return value from travel() directly:

let result2 = travel()("London")

SAVE 50% To celebrate Black Friday, all our books and bundles are half price, so you can take your Swift knowledge further without spending big! Get the Swift Power Pack to build your iOS career faster, get the Swift Platform Pack to builds apps for macOS, watchOS, and beyond, or get the Swift Plus Pack to learn advanced design patterns, testing skills, and more.

Save 50% on all our books and bundles!

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