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// Two related class types.

class Base{}

class Derived : Base{}

class Program

{

static void Main()

{

// Implicit cast between derived to base.

Base myBaseType;

myBaseType = new Derived();

// Must explicitly cast to store base reference

// in derived type.

Derived myDerivedType = (Derived)myBaseType;

}

}

This explicit cast works due to the fact that the Base and Derived classes are related by classical

inheritance. However, what if you have two class types in 

different hierarchies with no common

parent (other than System.Object) that requires conversions? Given that they are not related by

classical inheritance, explicit casting offers no help.

On a related note, consider value types (e.g., structures). Assume you have two .NET structures

named Square and Rectangle. Given that structures cannot leverage classic inheritance (as they are

always sealed), you have no natural way to cast between these seemingly related types.

While you could build helper methods in the structures (such as Rectangle.ToSquare()), C#

allows you to build custom conversion routines that allow your types to respond to the () casting

operator. Therefore, if you configured the structures correctly, you would be able to use the follow-

ing syntax to explicitly convert between them as follows: