多态

原来多态不仅仅是方法

1、方法多态

2、属性多态

public class Contact
{
     public virtual string Email { get; set; }
}

public class Customer : Contact
{
     public override string Email
      {
          get
          {
              return base.Email;
          }
          set 
          {
              base.Email = value;
          }
      }
}

3、索引器多态

 public class SiteList
    {

        protected string[] sites = new string[5];

        public virtual string this[int index]
        {
            get
            { 
                return sites[index];
            }
            set
            {
                sites[index] = value;
            }
        }
    }

public class FinancialSiteList : SiteList
    {
        public override string this[int index]
        {
            get
            {
                if (index > sites.Length)
                {
                    return (string)null;
                }
                return base[index];
            }
            set
            {
                base[index] = value;
            }
        }
    }