WWDC24 SALE: Save 50% on all my Swift books and bundles! >>

What does an exclamation mark mean?

Swift version: 5.10

Paul Hudson    @twostraws   

Swift uses exclamation marks to signal both force unwrapping of optionals and explicitly unwrapped optionals. The former means "I know this optional variable definitely has a value, so let me use it directly." The latter means "this variable is going to be nil initially then will definitely have a value afterwards, so don't make me keep unwrapping it."

Broadly speaking, using exclamation marks is frowned upon because "trust me it's safe" isn't as good as the compiler absolutely enforcing it. That being said, it's your code: if you know something cannot be nil (usually because if it were nil your program would explode!) then do what works best.

Save 50% in my WWDC sale.

SAVE 50% To celebrate WWDC24, 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!

Available from iOS 7.0 – see Hacking with Swift tutorial 1

Similar solutions…

About the Swift Knowledge Base

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

BUY OUR BOOKS
Buy Pro Swift Buy Pro SwiftUI 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 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 Beyond Code

Was this page useful? Let us know!

Average rating: 4.6/5

 
Unknown user

You are not logged in

Log in or create account
 

Link copied to your pasteboard.