gistfile1.cs

 public class AddressBook
 {
     public IEnumerable<Contact> Contacts
     {
         get { return _contacts; }
     }
 
     public AddressBook()
     {
         _contacts = new List();
     }
 
     private IList<Contact> _contacts;
 
     public void AddContact(Contact contact)
     {
         _contacts.Add(contact);
     }
 }