fragile-subclass-problem/4/fragile.cs - The revised version with method A.M2 being hidden.

Lecture 8 - slide 32 : 37 Program 6

// Non-Dangerous program.
// Compiles and runs.
// M2 is declared new in B.
// A.M2 is not virtual.

using System;

// New version of A
class A {

  public void M1(){
    Console.WriteLine("Method 1");
    this.M2();
  }

  // New method in this version.
  // Same name as the dangerous operation in subclass B
  // M2 is not virtual.
  public void M2(){
    Console.WriteLine("M2 in new version of A");
  }

}

class B: A {

  public  new  void M2(){
    Console.WriteLine("Dangerous Method 2");
  }
}

class Client{
  
  public static void Main(){
    A a = new B();
    B b = new B();

    a.M1();  // Nothing dangerous expected
             // Will call a.M2 - the non-dangerous version

    a.M2();  // Makes sense when M2 exists in class A
             // Will call a.M2 - the non-dangerous version

    b.M2();  // Expects dangerous operation
  }
}