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

Trailing closure syntax

If the last parameter to a function is a closure, Swift lets you use special syntax called trailing closure syntax. Rather than pass in your closure as a parameter, you pass it directly after the function inside braces.

To demonstrate this, here’s our travel() function again. It accepts an action closure so that it can be run between two print() calls:

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

Because its last parameter is a closure, we can call travel() using trailing closure syntax like this:

travel() {
    print("I'm driving in my car")
}

In fact, because there aren’t any other parameters, we can eliminate the parentheses entirely:

travel {
    print("I'm driving in my car")
}

Trailing closure syntax is extremely common in Swift, so it’s worth getting used to.

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: 4.3/5