Swiftのシングルトンパターンでリセットもできる実装 ref: http://qiita.com/hayakawatomoaki/items/22e631dfb9ebf9e8d578

file0.txt

class User {

    private struct Static {
        static var instance: User?
    }

    class var sharedInstance: User {
        if let instance = Static.instance {
            return instance
        }
        Static.instance = User()
        return Static.instance!
    }

    func deleteSharedInstance() {
        Static.instance = nil
    }




    var i = 0

    func increment() {
        i++
    }
}

file1.txt

class User {

    private static var instance: User?

    class var sharedInstance: User {
        if let instance = instance {
            return instance
        }
        instance = User()
        return instance!
    }

    func deleteSharedInstance() {
        User.instance = nil
    }



    var i = 0

    func increment() {
        i++
    }
}

file2.txt

User.sharedInstance.increment() // 1
User.sharedInstance.increment() // 2
User.sharedInstance.increment() // 3
User.sharedInstance.increment() // 4
User.sharedInstance.increment() // 5

User.sharedInstance.deleteSharedInstance()

User.sharedInstance.increment() // 1
User.sharedInstance.increment() // 2