NEW! Master Swift design patterns with my latest book! >>

< Previous: Trailing closure syntax   Next: Using closures as parameters when they return values >

Using closures as parameters when they accept parameters

This is where closures can start to be read a bit like line noise: a closure you pass into a function can also accept its own parameters.

We’ve been using () -> Void to mean “accepts no parameters and returns nothing”, but you can go ahead and fill the () with the types of any parameters that your closure should accept.

To demonstrate this, we can write a travel() function that accepts a closure as its only parameter, and that closure in turn accepts a string:

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

Now when we call travel() using trailing closure syntax, our closure code is required to accept a string:

travel { (place: String) in
    print("I'm going to \(place) in my car")
}

Learn Server-Side Swift now!

Take your Swift code to the server and become a full-stack developer with my latest book: Server-Side Swift!

< Previous: Trailing closure syntax   Next: Using closures as parameters when they return 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!

Average rating: 5.0/5

Click here to visit the Hacking with Swift store >>