Don’t return — NEVER in Swift

Not nil, not null

Photo by David Besh on Unsplash

Prerequisites:

You will need to be familar with the basics of Swift and able to start a Playground (or similar)

Terminology

Never: a return type for a function (or closure, or method) that will never terminate

The source of this article

I began looking at **Combine** after a voiding it for some time. Hidden in one of WWDC19’s videos is the following code snippet for **Subscribers**

extension Subscribers {
class Assign<Root, Input>: Subscriber, Cancellable {
typealias Failure = Never
init(object: Root, keyPath: ReferenceWritableKeyPath<Root, Input>)
}
}

Where we are told

‘Because in Swift there is no way to handle an error when you are just writing a property value, we set the failure type of assign to Never’

Wait, what are you talking about?

The documentation

Apple’s documentation to the rescue (sort of).

They describe `Never` as a return type for a function (or closure, or method) that…