NEW: Got a question? Get help on our new forums! >>

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")
Hacking with Swift is sponsored by Instabug

SPONSORED Catch bugs as soon as they happen and know exactly why a crash occurred by integrating Instabug's SDK in one minute. You will automatically receive device data, network logs, and reproduction steps with every bug and crash report.

Learn more and get started for free

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

Support my work on Patreon

BUY OUR BOOKS
Buy Pro Swift Buy Swift Design Patterns Buy Testing Swift Buy Hacking with iOS Buy Swift Coding Challenges Buy Swift on Sundays Volume One Buy Server-Side Swift (Vapor Edition) Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Advanced iOS Volume Three Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with macOS Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Server-Side Swift (Kitura Edition) Buy Beyond Code

Was this page useful? Let us know!

Average rating: 4.1/5