NEW: Get your ticket for Hacking with Swift Live 2019! >>

What's the difference between let and var?

Swift version: 5.0

Paul Hudson    @twostraws   

Swift lets you create both variables and constants as ways to reference your data, but there's a strong push (even Xcode warnings!) if you create things as variables then never change them. To make a constant, use let like this:

let x = 10

To make a variable, use var like this:

var y = 20

The reason Swift strongly encourages you to use constants wherever possible is because it's safer: if you say "this value will never change," then Swift will refuse to let you change it even by accident. It also opens the possibility of compiler optimizations if the system knows certain data will not change.

HACKING WITH SWIFT LIVE This July is a new two-day event where you'll be inspired by great speakers on day one then learn all the amazing new features from WWDC on day two – click here for more information and tickets.

Available from iOS 7 – 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!

Click here to visit the Hacking with Swift store >>