Code snippet for the blog post https://sriramsakthivel.wordpress.com/2015/01/11/breaking-the-clr-type-safety-part-two-2/

breaking-the-clr-type-safety-part-two.cs

class A
{
    protected int x = 123;
}
class B : A
{
    static void Main()
    {
        A a = new A();
        B b = new B();

        // Error CS1540, because x can only be accessed by
        // classes derived from A.
        // a.x = 10;

        // OK, because this class derives from A.
        b.x = 10;
    }
}