How do you create custom notifications in Swift 3?

In Objective-C, a custom notification is just a plain NSString, but it's not obvious in the WWDC version of Swift 3 just what it should be.

There is a cleaner (I think) way to achieve it

extension Notification.Name {

    static let onSelectedSkin = Notification.Name("on-selected-skin")
}

And then you can use it like this

NotificationCenter.default.post(name: .onSelectedSkin, object: selectedSkin)

You could also use a protocol for this

protocol NotificationName {
    var name: Notification.Name { get }
}

extension RawRepresentable where RawValue == String, Self: NotificationName {
    var name: Notification.Name {
        get {
            return Notification.Name(self.rawValue)
        }
    }
}

And then define your notification names as an enum anywhere you want. For example:

class MyClass {
    enum Notifications: String, NotificationName {
        case myNotification
    }
}

And use it like

NotificationCenter.default.post(name: Notifications.myNotification.name, object: nil)

This way the notification names will be decoupled from the Foundation Notification.Name. And you will only have to modify your protocol in case the implementation for Notification.Name changes.