How to specify default values for dictionary keys
Swift version: 5.6
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]
SPONSORED Join a FREE crash course for mid/senior iOS devs who want to achieve an expert level of technical and practical skills – it’s the fast track to being a complete senior developer! Hurry up because it'll be available only until April 28th.
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…
- How to sort the keys of your JSON using Codable
- How to specify floating-point precision in a string
- How to specify the Dynamic Type sizes a view supports
- How to specify your own date format with Codable and JSONEncoder
- How to transform a dictionary using mapValues()
About the Swift Knowledge Base
This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.
