关于IEnumerable，大家帮我看看
下面是下载的关于IEnumerable的实例，我看不懂，哪位大哥帮忙解释下，讲讲如何实现IEnumerable接口，谢了
class Employees : IEnumerable
{
private ArrayList m_Employees;
private int m_MaxEmployees;

public Employees( int MaxEmployees )
{
m_MaxEmployees = MaxEmployees;
m_Employees = new ArrayList( MaxEmployees );
}

// Here is the implementation of the indexer by array index
public Employee this[int index]
{
get
{
// Check for out of bounds condition
if ( index < 0 || index > m_Employees.Count - 1 )
return null;

// Return employee based on index passed in
return (Employee) m_Employees[index];
}

set
{
// Check for out of bounds condition
if ( index < 0 || index > m_MaxEmployees-1 )
return;

// Add new employee
m_Employees.Insert( index, value );
}
}

// Here is the implementation of the indexer by SSN
public Employee this[string SSN]
{
get
{
Employee empReturned = null;

foreach ( Employee employee in m_Employees )
{
// Return employee based on index passed in
if ( employee.SSN == SSN )
{
empReturned = employee;
break;
}
}

return empReturned;
}
}

// Return the total number of employees.
public int Length
{
get
{
return m_Employees.Count;
}
}

// IEnumerable implementation, delegates IEnumerator to
// the ArrayList
public IEnumerator GetEnumerator()
{
return m_Employees.GetEnumerator();
}
}

class Employee
{
private string m_firstName;
private string m_middleName;
private string m_lastName;
private string m_SSN;

// Constructor
public Employee( string FirstName, string LastName, string
MiddleName, string SSN )
{
m_firstName = FirstName;
m_middleName = MiddleName;
m_lastName = LastName;
m_SSN = SSN;
}

// FirstName property
public string FirstName
{
get { return m_firstName; }
set { m_firstName = value; }
}

// MiddleName property
public string MiddleName
{
get { return m_middleName; }
set { m_middleName = value; }
}

// LastName property
public string LastName
{
get { return m_lastName; }
set { m_lastName = value; }
}

// SSN property
public string SSN
{
get { return m_SSN; }
set { m_SSN = value; }
}
}

[解决办法]
你可以像数组一样操作Employees

Employees[i]
Employees.Length

继承IEnumerable 就是提供这样的功能.

[解决办法]
错了，这个例子不是很好
IEnumerable是为foreach量身定做的
核心方法就是GetEnumerator，用来获得一个IEnumarator的实例。
（例子中没有这个部分的实现，所以说不好。）

至于索引器、Length这些都和IEnumerable无关
[解决办法]
不是像数组一样，那是this索引器的功能

这个接口是你可以在你的类实例上使用foreach来枚举