using System;

​

interface Runnable {

    void Run(string details);

}

​

abstract class RunnableBase : Runnable {

    public virtual void Run(string more) {

        Console.WriteLine(more);

    }

}

​

class Impl1 : RunnableBase {

    public override void Run(string extra) {

        base.Run(extra);

    }

}

​

class Impl2 : RunnableBase {

    public override void Run(string other) {

        base.Run(other);

    }

}

​

var random = new Random();

​

Runnable GetRunnable() {

    if (random.Next(2) == 0) {

        return new Impl1();

    }

    else {

        return new Impl2();

    }

}

​

var runnable = GetRunnable();

runnable.Run(details: "details");