How can I implement static methods on an interface?

Question

I have a 3rd party C++ DLL that I call from C#.

The methods are static.

I want to abstract it out to do some unit testing so I created an interface with the

Answer 1

Interfaces can't have static members and static methods can not be used as implementation of interface methods.

What you can do is use an explicit interface implementation:

public interface IMyInterface
{
    void MyMethod();
}

public class MyClass : IMyInterface
{
    static void MyMethod()
    {
    }

    void IMyInterface.MyMethod()
    {
        MyClass.MyMethod();
    }
}

Alternatively, you could simply use non-static methods, even if they do not access any instance specific members.

Answer 2

Static members are perfectly legal in the CLR, just not C#.

You could implement some glue in IL to link up the implementation details.

Not sure if the C# compiler would allow calling them though?

See: 8.9.4 Interface type definition ECMA-335.

Interface types are necessarily incomplete since they say nothing about the representation of the values of the interface type. For this reason, an interface type definition shall not provide field definitions for values of the interface type (i.e., instance fields), although it can declare static fields (see §8.4.3).

Similarly, an interface type definition shall not provide implementations for any methods on the values of its type. However, an interface type definition can—and usually does—define method contracts (method name and method signature) that shall be implemented by supporting types. An interface type definition can define and implement static methods (see §8.4.3) since static methods are associated with the interface type itself rather than with any value of the type.