FREE: Watch my new YouTube videos, Xcode in 20 Seconds! >>

What is optional chaining?

Paul Hudson       @twostraws

Optional chaining is a Swift feature that allows execution of a statement to stop and return nil at any point. For example, all views have an optional superview property that stores whichever UIView contains it, all UIView has an optional gestureRecognizer array that stores the gesture recognizers it has, and all arrays have an optional first property that returns the first item.

Optional chaining allows us to put those three optionals together like this:

let firstParentRecognizer = view.superview?.gestureRecognizers?.first

So, superview is optional, gestureRecognizers is optional, and first is optional, but the end result – firstParentRecognizer will be a simple UIGestureRecognizer? rather than a triple optional. The optional chaining – the two question marks – mean that if superview is nil then firstParentRecognizer gets set to nil and the rest of the statement is ignored, and the same is true of gestureRecognizers.

Without optional chaining we’d need to use a pyramid of if let statements, like this:

if let superview = view.superview {
    if let recognizers = superview.gestureRecognizers {
        let firstParentRecognizer = recognizers.first
    }
}

Sponsored You’re already busy updating your app for Swift 4.2 and iOS 12, so why not let Instabug help you find and fix bugs? Add just two lines of code to your project and receive comprehensive reports with all the feedback you need to ship a world-class app – click here to learn more!

Available from iOS 8.0

Did this solution work for you? Please pass it on!

Other people are reading…

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.

Get the ultimate experience

The Swift Power Pack includes my first six books for one low price, helping you jumpstart a new career in iOS development – check it out!

MASTER SWIFT NOW
Buy Testing Swift Buy Practical iOS 12 Buy Pro Swift Buy Swift Design Patterns 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 Advanced iOS Volume Two 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 >>