Swift - Prevent creating two reference of class [duplicate]

Question

I have app delegate which is a single point in app. Also I've created ApplicationManager class which is a part of app delegate now.

so what I want to achieve is to protect my code from other developers to be used in a wrong way.

So let's say my ApplicationManager looks like this:

class ApplicationManager {

    var api: API?

    static func instance() -> ApplicationManager {
        guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else {
            fatalError()
        }
        return appDelegate.applicationManager
    }
}

I want to make sure that used will use ApplicationManager via:

let am = ApplicationManager.instance() but not like this am = ApplicationManager() which will create one more manager which I don't want.

is there a way to show build time error? or drop some message? or crash in crash in case there are more that one ApplicationManager in app =)

Answer 1

Simply make your init private:

private init() {}

Also, the singleton pattern would be usually implemented simply as:

static let shared = ApplicationManager()

Called as ApplicationManager.shared. If you want AppDelegate to create the instance, private init won't work.