Expressing Designs in C# - Effective C# - page 137

// other details elided
private string vendorName;
}
The Employee, Customer, and Vendor classes should not share a common
base class. But they do share some properties: names (as shown earlier),
addresses, and contact phone numbers. You could factor out those prop-
erties into an interface:
public interface IContactInfo
{
string Name { get ; }
PhoneNumber PrimaryContact { get ; }
PhoneNumber Fax { get ; }
Address PrimaryAddress { get ; }
}
public class Employee : IContactInfo
{
// implementation elided.
}
This new interface can simplify your programming tasks by letting you
build common routines for unrelated types:
public void PrintMailingLabel( IContactInfo ic)
{
// implementation deleted.
}
This one routine works for all entities that implement the IContactInfo
interface. Customer, Employee, and Vendor all use the same routine—but
only because you factored them into interfaces.
Using interfaces also means that you can occasionally save an unboxing
penalty for structs . When you place a struct in a box, the box supports
all interfaces that the struct supports. When you access the struct
through the interface pointer, you don't have to unbox the struct to
access that object. To illustrate, imagine this struct that defines a link and
a description:
public struct URLInfo : IComparable < URLInfo >, IComparable
{