using System;
using System.Collections.Generic;

namespace YieldReturn
{
    class Program
    {
        static void Main(string[] args)
        {
            var list = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9 };

            var resultNormal = EvenNormal(list);
            foreach (var item in
 
 resultNormal)
            {
                Console.WriteLine(item);
            }

            var resultYieldReturn = EvenYieldReturn(list);
            foreach (var item in resultYieldReturn)
            {
                Console.WriteLine(item);
            }
        }

        static IEnumerable<int
 
> EvenNormal(List<int> list)
        {
            var result = new List<int>();
            foreach (var item in list)
            {
                if (item % 2 == 0)
                {
                    result.Add(item);// 類似DataSet（整個結果集加載到內存中），適合少量數據的遍歷
                }
            }
            
 
return result;
        }

        static IEnumerable<int> EvenYieldReturn(List<int> list)
        {
            foreach (var item in list)
            {
                if (item % 2 == 0)
                {
                    yield return item;// 類似DataReader（讀取一條返回一條），適合海量數據的遍歷
                }
            }
            yield break;
        }
    }
}

C#中yield return的用法示例