Derived class should always be singleton

Question

I am trying to create a base class with some functionality shared between all derived classes. And all derived classes should be Singletons. Below a pseudo example.

class ExtensionSettings
{
    public string GetConfigHtml()
    {
        // creat conifig html for all properties
    }

    public void SaveSettings()
    {
        // save stuff
    }
}

class SettingsA : ExtensionSettings
{
    private static SettingsA instance;
    public static SettingsA Instance {get {return instance ?? (instance = new SettingsA());}}

    public string setting1{get;set;}
    public string setting2{get;set;}
}

class SettingsB : ExtensionSettings
{
    private static SettingsB instance;
    public static SettingsB Instance {get {return instance ?? (instance = new SettingsB());}}

    public string setting1{get;set;}
    public string setting2{get;set;}
}


static void Main(string[] args)
{
    System.Console.WriteLine(SettingsA.Instance.setting1);
    System.Console.WriteLine(SettingsB.Instance.setting2);
}

Is it possible to move the instancing part to the ExtensionSettings base class?

Answer 1

base class doesn't know about the rest of the object to be instantiated. basically, when you derive from a base class, the extra logic added in derived class is hidden from base class. therefore, doing instantiation in the base class is not possible.