How to force abstract class childs to implement a static method? [duplicate]

Question

Possible Duplicate:
How can I force inheriting classes to implement a static method in C#?

I understand abstract and static are opposite, but I want to force derived classes to implement a static method. how can I do that?

Edit after SimonC : While trying to describe what I want to do, i realized that static methods of super class will not be able to call the overridden subclass version.

But olivier's alternative solution looks nice.

Answer 1

A possible approach of combining a static behavior with inheritance or interface implementation is to use the singleton pattern. The access to a singleton object is static, but the object is created with new like a "normal" object

public interface ISomeInterface { ... }

public class SomeClass : ISomeInterface
{ 
    public static readonly SomeClass Instance = new SomeClass();

    private SomeClass()
    { 
    }

    // TODO: Implement ISomeInterface
    // and/or override members from a base class.
}

---

Accessing a method of the singleton

ISomeInterface obj = SomeClass.Instance; // Static access to interface.
var y = obj.SomeMethod(x);