NEW: Subscribe to Hacking with Swift+ and accelerate your learning! >>

Force unwrapping

Optionals represent data that may or may not be there, but sometimes you know for sure that a value isn’t nil. In these cases, Swift lets you force unwrap the optional: convert it from an optional type to a non-optional type.

For example, if you have a string that contains a number, you can convert it to an Int like this:

let str = "5"
let num = Int(str)

That makes num an optional Int because you might have tried to convert a string like “Fish” rather than “5”.

Even though Swift isn’t sure the conversion will work, you can see the code is safe so you can force unwrap the result by writing ! after Int(str), like this:

let num = Int(str)!

Swift will immediately unwrap the optional and make num a regular Int rather than an Int?. But if you’re wrong – if str was something that couldn’t be converted to an integer – your code will crash.

As a result, you should force unwrap only when you’re sure it’s safe – there’s a reason it’s often called the crash operator.

Hacking with Swift is sponsored by NSSpain

SPONSORED Announcing NSSpain 2020: Remote Edition! An online, continuous conference for iOS developers. We’ll start on Thursday and finish on Friday, with talks, activities, and lots of fun for 36 hours, non-stop. Sound good? Join us!

Find out 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!

Average rating: 4.7/5

Link copied to your pasteboard.