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.

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!