FREE: Read a new Swift article every day – click here! >>

< Previous: Implicitly unwrapped optionals   Next: Optional chaining >

Nil coalescing

The nil coalescing operator unwraps an optional and returns the value inside if there is one. If there isn’t a value – if the optional was nil – then a default value is used instead. Either way, the result won’t be optional: it will either by the value from inside the optional or the default value used as a back up.

Here’s a function that accepts an integer as its only parameter and returns an optional string:

func username(for id: Int) -> String? {
    if id == 1 {
        return "Taylor Swift"
    } else {
        return nil
    }
}

If we call that with ID 15 we’ll get back nil because the user isn’t recognized, but with nil coalescing we can provide a default value of “Anonymous” like this:

let user = username(for: 15) ?? "Anonymous"

That will check the result that comes back from the username() function: if it’s a string then it will be unwrapped and placed into user, but if it has nil inside then “Anonymous” will be used instead.

Get my latest video for free

Learn about value types, functional programming, and protocol-oriented programming in this new video – it's free!

< Previous: Implicitly unwrapped optionals   Next: Optional chaining >
MASTER SWIFT NOW
Buy Testing Swift Buy Practical iOS 12 Buy Pro Swift Buy Swift Design Patterns Buy Swift Coding Challenges Buy Server-Side Swift (Vapor Edition) Buy Server-Side Swift (Kitura Edition) Buy Hacking with macOS Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with Swift Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Beyond Code

Was this page useful? Let me know!

Click here to visit the Hacking with Swift store >>