NEW: Get your ticket to Hacking with Swift Live 2020! >>

What's the difference between let and var?

Swift version: 5.1

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.

SPONSORED Why the top iOS apps rely on Instabug for crash reporting. Crash reporting + Bug reporting + Customizable in-app surveys all in one SDK. Know which line of code caused the crash along with network logs, repro steps, and the session profiler to identify and resolve severe crashes quickly. See more detailed features comparison and try Instabug for free here.

Listen to the Swift over Coffee podcast

Available from iOS 7 – 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 Swift Design Patterns Buy Testing Swift Buy Hacking with iOS Buy Swift Coding Challenges Buy Swift on Sundays Volume One Buy Server-Side Swift (Vapor Edition) 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 Server-Side Swift (Kitura Edition) Buy Beyond Code

Was this page useful? Let us know!

Average rating: 3.5/5