C# 0 The Complete Reference

Base Class References and Derived Objects

As you know, C# is a strongly typed language. Aside from the standard conversions and 

automatic promotions that apply to its value types, type compatibility is strictly enforced. 

Therefore, a reference variable for one class type cannot normally refer to an object of 

another class type. For example, consider the following program that declares two classes 

that are identical in their composition:

// This program will not compile.

class X {

  int a;

  public X(int i) { a = i; }

}

class Y {

  int a;

  public Y(int i) { a = i; }

}

class IncompatibleRef {

  static void Main() {

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    X x = new X(10);

    X x2;

    Y y = new Y(5);

    x2 = x; // OK, both of same type

    x2 = y; // Error, not of same type

  }

}

Here, even though class