NEW: Learn SwiftUI with my free YouTube video series! >>

What does weak mean?

Swift version: 5.0

Paul Hudson    @twostraws   

Unless you specific otherwise, all Swift properties are strong, which means they will not be removed from RAM until whatever owns them is removed from RAM. So, if you create an array in your view controller and you want it to stick around until the view controller is destroyed, that's what strong does.

Weak on the other hand is there when you want to say "I want to be able to reference this variable, but I don't mind if it goes away, so I don't want to own it." This might seem strange: after all, where's the point in having a reference to a variable that might not be there?

Well, the answer lies in a thing called reference cycles. If object A has a strong variable pointing at object B, and object B has a strong variable pointing at object A, neither object would ever be deleted because they both keep each other alive.

In this situation, having one of the objects change their property to be weak would solve the problem. For example, object A has a strong variable to object B, but object B has a weak variable pointing at object A. This guarantees that B cannot be destroyed while A still exists, but A can be destroyed because B doesn't have a strong variable owning it.

SPONSOR Meet the new Instabug – more than just bug reporting! We help you build better apps and minimize your debugging time. With each bug report, we automatically capture details like network requests, repro steps, and session details. Get real-time crash reports with stack trace details and session data to help you catch and fix issues easily. And with our customizable in-app surveys, you’ll gather insightful user feedback and much more. Instabug is the fastest and easiest way to release with confidence. Start your free trial now! Start your free trial now!

Available from iOS 7.0 – see Hacking with Swift tutorial 1

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.

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!

Average rating: 4.2/5

Click here to visit the Hacking with Swift store >>