Access Virtual Function In Interface Directly From Implemented Class

Question

Say I have the following function:

public interface MyInterface
{
    int GetNumber();
    virtual int GetTwiceNumber()
        => 2 * GetNumber();
}

I can implement the interface in a class as such:

public class MyClass
    : MyInterface
{
    public int GetNumber()
        => 5;
}

I can access the GetNumber function directly through the class, but I have to access the GetTwiceNumber function by reinterpreting MyClass as MyInterface:

MyClass myObject = new();
Console.WriteLine(((MyInterface)myObject).GetTwiceNumber());

Output:

10

I want to make MyInterface.GetTwiceNumber directly accessible from the class. In this example, I could probably just copy the code for the function to the class, but for larger functions this would be impractical. Additionally, if one function were edited, and the other was not, this could cause errors that would be difficult to trace.

I thought of:

public int GetTwiceNumber()
    => 2 * ((MyInterface)this).GetNumber();

However, the issue with this is that once I create a function in my class with the same name as the implemented virtual function, it will override the virtual function, disallowing me from accessing the virtual function defined in the interface. As a result, the code above will just throw a StackOverloadException.

How can I allow a virtual function defined in an interface to be directly accessible though an implemented class, rather than requiring the user to reinterpret the class as that interface, given that the class does not already override the virtual function?

Answer 1

There is no possible way to configure this in the class or interface.

However, if you are willing to sacrifice the descendent class's ability to override the method, you can use extension methods:

public static class MyInterfaceExtensions
{
    public static int GetTwiceNumber(this MyInterface myInterface)
        => 2 * myInterface.GetNumber();
}