C#通过提供索引器，可以象处理数组一样处理对象。特别是属性，每一个元素都以一个get或set方法暴露。
public class Skyscraper
{
Story[] stories;
public Story this [int index]
{
get
{
return stories [index];
}
set
{
if (value != null)
{
stories [index] = value;
}
}
}
//...
}
Skyscraper empireState = new Skyscraper (/*...*/);
empireState [102] = new Story ("The Top One", /*...*/);
