NEW: Nominations are now open for the 2019 Swift Community Awards! >>

Why is immutability important?

Swift version: 5.1

Paul Hudson    @twostraws   

Swift developers rely heavily on constants rather than variables, to the point where Xcode even warns you if you create a variable then never change it. There are three main reasons why immutability is important in Swift, and I want to walk through them briefly.

First, immutability makes your code easier to reason about. If you use constants everywhere, you know for sure that your data can’t be changed by surprise by some other part of your program – in fact, it can’t be changed at all. This also makes multi-threaded code significantly easier to think about.

Second, it stops you making silly mistakes. When you use a constant rather than a variable, Swift won’t let you change that constant no matter how hard you try – it’s like you’ve made a contract with yourself.

Third, Swift can optimize it more efficiently. If Swift knows a value can’t be changed, it can in theory store your data in a more efficient way.

SAVE 20% ON iOS CONF SG The largest iOS conference in Southeast Asia is back in Singapore for the 5th time in January 2020, now with two days of workshops plus two days of talks on SwiftUI, Combine, GraphQL, and more! Save a massive 20% on your tickets by clicking on this link.

Available from iOS 8.0 – learn more in my book Pro Swift

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.

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 us know!

Average rating: 5.0/5