GO FURTHER, FASTER: Try the Swift Career Accelerator today! >>

What’s the difference between a static variable and a class variable?

Swift version: 5.10

Paul Hudson    @twostraws   

Both the static and class keywords allow us to attach variables to a class rather than to instances of a class. For example, you might create a Student class with properties such as name and age, then create a static numberOfStudents property that is owned by the Student class itself rather than individual instances.

Where static and class differ is how they support inheritance: When you make a static property it becomes owned by the class and cannot be changed by subclasses, whereas when you use class it may be overridden if needed.

For example, here’s a Person class with one static property and one class property:

class Person {
    static var count: Int {
        return 250
    }

    class var averageAge: Double {
        return 30
    }
}

If we created a Student class by inheriting from Person, trying to override count (the static property) would fail to compile if uncommented, whereas trying to override averageAge (the class property) is OK:

class Student: Person {
    // THIS ISN'T ALLOWED
    // override static var count: Int {
    //    return 150
    // }

    // THIS IS ALLOWED
    override class var averageAge: Double {
        return 19.5
    }
}
Hacking with Swift is sponsored by RevenueCat.

SPONSORED Take the pain out of configuring and testing your paywalls. RevenueCat's all new Paywall Editor allow you to remotely configure your paywall view without any code changes or app updates.

Click to save your free spot now

Sponsor Hacking with Swift and reach the world's largest Swift community!

Available from iOS 8.0

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 Interview Challenges Buy Swift on Sundays Volume One Buy Server-Side Swift 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.