NEW: Subscribe to Hacking with Swift+ and accelerate your learning! >>

How to specify default values for dictionary keys

Swift version: 5.2

Paul Hudson    @twostraws   

Reading a dictionary key returns an option value by default, because the key you asked for might not exist. However, there’s a slightly different subscript you can call that eliminates optionality: when you read a key, you can also provide a default value to use if the key doesn’t exist.

For example, here’s a dictionary representing the high scores in a game:

var scores = ["Taylor Swift": 25, "Ed Sheeran": 20]

If we wanted to read the score of Adele Adkins, we’d get back nil because she doesn’t have a score. And if we tried to read any of the values that do have keys we’d still get back an optional integer.

Fortunately, if you provide a default value while reading a key you can be guaranteed you’ll always get a value back, so the return value for our scores dictionary will always be a real integer rather than an optional.

So, here we can read Adele’s score from the dictionary, or give it a default value of 0 if the key doesn’t exist:

var adeleScore = scores["Adele Adkins", default: 0]
Hacking with Swift is sponsored by Instabug

SPONSORED Are you tired of wasting time debugging your Swift app? Instabug’s SDK is here to help you minimize debugging time by providing you with complete device details, network logs, and reproduction steps with every bug report. All data is attached automatically, and it only takes a line of code to setup. Start your free trial now and get 3 months off exclusively for the Hacking with Swift Community.

Start your free trial!

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

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.

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: 4.9/5

Link copied to your pasteboard.