using System;

public class Program

{

    public static void Main()

    {

        var a = new A();

        var result = a.With(x => x.ValueB as B2).With(x => x.ValueC).With(x => x.ValueD);

        Console.WriteLine("Hello World");

    }

}

​

public static class Monades

{

    public static TResult With<TSource, TResult>(this TSource source, Func<TSource, TResult> selector) where TSource : class

    {

        if (source == null)

            return default(TResult);

        return selector(source);

    }

}

​

class A {

    public B ValueB;

}

​

class B {

    public C ValueC;

}

​

class B2 : B {

}

​

class C {

    public int ValueD;

}

​

​

​

​