Singleton closed for modification open to extend

Question

I would like to know how to achieve this: Assume I have a singleton class as

class Global{
    static let shared = Global()
    private init(){}
}

I want this class as closed to modification. But open to extend. I want to achieve result as Global.shared.var1

When var1 is coming from another class somehow extending Global.

It's a wish. Is it even possible? What is the right way to achieve this.

Answer 1

Found a hack that served my purpose for the time being (suggest me a better way/alternate):

class Students{
    static let shared = Students()
    private init(){}
    var name: [String] = ["Farhan","Hasan","Saba","Fatima"]
}
class Teachers{
    static let shared = Teachers()
    private init(){}
    var name: [String] = ["Mr. Riaz","Ms. Ayesha"]
}

//Base for Singleton, sort of proxy
class Global{
    private init(){}
}

//Somewhere else in your project
extension Global{
    static let students = Students.shared
}
//Somewhere else in your project
extension Global{
    static let teachers = Teachers.shared
}

//Apparently it served the purpose
print(Global.students.name) //prints: ["Farhan", "Hasan", "Saba", "Fatima"]
print(Global.teachers.name) //prints: ["Mr. Riaz", "Ms. Ayesha"]