When adding custom subscripts to a type, you can now use default arguments for any of the parameters. For example, if we had a PoliceForce
struct with a custom subscript to read officers from the force, we could add a default
parameter to send back if someone tries to read an index outside of the array’s bounds:
struct PoliceForce {
var officers: [String]
subscript(index: Int, default default: String = "Unknown") -> String {
if index >= 0 && index < officers.count {
return officers[index]
} else {
return `default`
}
}
}
let force = PoliceForce(officers: ["Amy", "Jake", "Rosa", "Terry"])
print(force[0])
print(force[5])
That will print “Amy” then “Unknown”, with the latter being caused because there is no officer at index 5. Note that you do need to write your parameter labels twice if you want them to be used, because subscripts don’t use parameter labels otherwise.
So, because I use default default
in my subscript, I can use a custom value like this:
print(force[-1, default: "The Vulture"])
SAVE 50% To celebrate WWDC23, all our books and bundles are half price, so you can take your Swift knowledge further without spending big! Get the Swift Power Pack to build your iOS career faster, get the Swift Platform Pack to builds apps for macOS, watchOS, and beyond, or get the Swift Plus Pack to learn advanced design patterns, testing skills, and more.
Download all Swift 5.2 changes as a playground Link to Swift 5.2 changes
Link copied to your pasteboard.