Swift’s strict initialization rules are great. They help prevent an entire category of bugs that were especially common in Objective-C. However, when working with Objective-C frameworks, particularly UIKit, these rules can be frustrating.

When you subclass UIViewController and UIView and provide your own initializer, the compiler will prompt you to add the following required initializer:

required init?(coder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
}

For view controllers, init(nibName:bundle:) is the designated initializer, but init(coder:) is required by the NSCoding protocol. It must be implemented not only because of the protocol, but because this is the initializer that Interface Builder calls when automatically instantiating UIViewController subclasses from storyboards or xibs. The same applies to UIView subclasses.

However, if you do not use Interface Builder, then init(coder:) is irrelevant and will never be called. It is annoying boilerplate. But the real problem is that Xcode (and presumably other editors) will offer init(coder:) as an auto-complete option when initializing your view or view controller. That is not ideal, because it is not a valid way to initialize your custom view or view controller. Luckily, you can use Swift’s @available attribute to prevent this, which also has the benefit of more clearly communicating that you should not use this initializer.

@available(*, unavailable)
required init?(coder: NSCoder) {
    fatalError("\(#function) has not been implemented")
}

Now, at compile-time, this initializer is inaccessible. Or technically, at “auto-complete while you type time”.

You might have the idea of putting this in an extension or a protocol, so that you can avoid typing the boilerplate for every UIView and UIViewController subclass. Unfortunately, that is not possible because required initializers must be provided in subclass declarations. So, using @available is the best we can do.

UPDATE: Thanks to JP for pointing out that there’s a SwiftLint rule for exactly this. Unfortunately, it does not currently support autocorrect.