using System.Collections.Generic;public class Stack<T>: IEnumerable<T>
{
T[] items; int count;
public void Push(T data) {} public T Pop() {} public IEnumerator<T> GetEnumerator() { for (int i = count – 1; i >= 0; --i) { yield return items[i];
} } public IEnumerable<T> TopToBottom { get { return this; } } public IEnumerable<T> BottomToTop { get { for (int i = 0; i < count; i++) { yield return items[i]; } } }
}TopToBottom 属性简单的返回this,因为statck本身就是enumerable,BottomToTop 用iterator返回了一个enumerable ,下面的例子展示如何使用这些属性来枚举栈中的成员.
using System;class Test{ static void Main() { Stack<int> stack = new Stack<int>(); for (int i = 0; i < 10; i++) stack.Push(i); foreach (int i in stack.TopToBottom) Console.Write("{0} ", i); Console.WriteLine(); foreach (int i in stack.BottomToTop) Console.Write("{0} ", i); Console.WriteLine(); }}当然这些属性也可以用在出foreach语句之外的地方,下面的例子展示了通过单独的Print 方法调用属性的结果.这个例子也展示了用iterator实现的含参的FromToBy 方法.
using System;using System.Collections.Generic;class Test{ static void Print(IEnumerable<int> collection) { foreach (int i in collection) Console.Write("{0} ", i); Console.WriteLine(); } static IEnumerable<int> FromToBy(int from, int to, int by) { for (int i = from; i <= to; i += by) { yield return i; } } static void Main() { Stack<int> stack = new Stack<int>(); for (int i = 0; i < 10; i++) stack.Push(i); Print(stack.TopToBottom); Print(stack.BottomToTop); Print(FromToBy(10, 20, 2)); }}范型或者非范型的enumerable interfaces 接口都包含唯一的成员无参和返回类型为enumerable interface的GetEnumerator 方法,一个enumerable 做为一个enumerator 工厂(factory),欠当地实现enumerables 保证每次调用GetEnumerator 方法时产生独立的enumerators,如果enumerable 内部的状态在两次调用GetEnumerator没有改变,两次返回的enumerators 应该是顺序相同的同一个数据集.这个必须得到保证即使enumerators的声明周期交迭.
using System;using System.Collections.Generic;class Test{ static IEnumerable<int> FromTo(int from, int to) { while (from <= to) yield return from++; } static void Main() { IEnumerable<int> e = FromTo(1, 10); foreach (int x in e) { foreach (int y in e) { Console.Write("{0,3} ", x * y); } Console.WriteLine(); } }}