NEW! Pre-order my latest book, Testing Swift! >>

< Previous: Closures with multiple parameters   Next: Capturing values >

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")

Download for free!

Want a free 75-minute video teaching functional programming, protocol-oriented programming, and more? This is your lucky day!

< Previous: Closures with multiple parameters   Next: Capturing values >
MASTER SWIFT NOW
Buy Practical iOS 12 Buy Pro Swift Buy Swift Design Patterns Buy Practical iOS 11 Buy Swift Coding Challenges Buy Server-Side Swift (Vapor Edition) Buy Server-Side Swift (Kitura Edition) Buy Hacking with macOS Buy Advanced iOS Volume One Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with Swift Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Beyond Code

Was this page useful? Let me know!

Click here to visit the Hacking with Swift store >>