What is the best practice to prevent an instance from init() in a Singleton class in Swift

Question

I learned from Using Swift with Cocoa and Objective-C that a singleton can be created like this:

class Singleton {
    static let sharedInstance = Singleton()
}

But as I learned, we should also prevent an instance created from the constructor. Creating an instance of the class Singleton outside the class scope, like the statement below, should be prevented:

let inst = Singleton()

So, could I do just like this:

class Singleton {
    static let sharedInstance = Singleton()
    private init() {}
}

Or, is there any better practice?

Answer 1

The way that you have suggested is the way that I always implemented it.

public class Singleton
{
    static public let sharedInstance = Singleton();

    private init()
    {

    }
}

It's the cleanest solution for a Singleton pattern that I've ever found. Now that in Swift 2 you can specify accessibility it does actually prevent you from calling something like:

var mySingleton = Singleton();

Doing so results in a compile time error:

'Singleton' cannot be constructed because it has no accessible initializers