Swift Dictionary default value

Question

A pattern I\'ve gotten used to with Python\'s defaultdicts is a dictionary that returns a default value if the value for a given key has not been explicitly set. Trying to d

Answer 1

This changed in Swift 4, and there's now a way to read a key's value or provide a default value if the key isn't present. For example:

let person = ["name": "Taylor", "city": "Nashville"]
let name = person["name", default: "Anonymous"]

This is particularly useful when modifying dictionary values, because you can write code like this:

var favoriteTVShows = ["Red Dwarf", "Blackadder", "Fawlty Towers", "Red Dwarf"]
var favoriteCounts = [String: Int]()

for show in favoriteTVShows {
    favoriteCounts[show, default: 0] += 1
}

I covered this change and others in my article What's new in Swift 4.