FREE TRIAL: Accelerate your app development career with Hacking with Swift+! >>

How do you return a value from a closure that takes no parameters?

Paul Hudson    @twostraws   

Closures in Swift have a distinct syntax that really separates them from simple functions, and one place that can cause confusion is how we accept and return parameters.

First, here’s a closure that accepts one parameter and returns nothing:

let payment = { (user: String) in
    print("Paying \(user)…")
}

Now here’s a closure that accepts one parameter and returns a Boolean:

let payment = { (user: String) -> Bool in
    print("Paying \(user)…")
    return true
}

If you want to return a value without accepting any parameters, you can’t just write -> Bool in – Swift won’t understand what you mean. Instead, you should use empty parentheses for your parameter list, like this:

let payment = { () -> Bool in
    print("Paying an anonymous person…")
    return true
}

If you think about it, that works just the same as a standard function where’d write func payment() -> Bool.

Hacking with Swift is sponsored by Essential Developer

SPONSORED Join a FREE crash course for iOS devs who want to become complete senior developers — from October 18th to 24th. Learn how to apply iOS app architecture patterns through a series of lectures and practical coding sessions.

Learn more

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

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!

 
Unknown user

You are not logged in

Log in or create account
 

Link copied to your pasteboard.