Pro C# 2010 and the .NET 4 Platform, Fifth Edition

6.6. Understanding Base Class/Derived Class Casting Rules

Now that you can build a family of related class types, you need to learn the rules of class casting operations. To do so, let's return to the Employees hierarchy created earlier in this chapter. Under the .NET platform, the ultimate base class in the system is System.Object. Therefore, everything "is-a" Object and can be treated as such. Given this fact, it is legal to store an instance of any type within an object variable:

void CastingExamples()
{
  // A Manager "is-a" System.Object, so we can

// store a Manager reference in an object variable just fine.
  object frank = new Manager("Frank Zappa", 9, 3000, 40000, "111-11-1111", 5);
}

In the Employees example, Managers, SalesPerson, and ...