yield return关键字其实相当于 list

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;

namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {
            DataTable dt = AddUserInfo();
            IEnumerable<UserInfo> i = GetUserInfoByYield(dt);
            foreach (var ii in i)
            {
                Console.WriteLine(ii.Name + ii.Age + ii.Address);
            }


            List<UserInfo> u = GetUserInfoByList(dt);
            foreach (var ii in i)
            {
                Console.WriteLine(ii.Name + ii.Age + ii.Address);
            }

            Console.Read();
        }

        public static DataTable AddUserInfo()
        {
            DataTable userInfo = new DataTable("UserInfo");
            DataColumn Name = new DataColumn("Name");
            DataColumn Age = new DataColumn("Age");
            DataColumn Address = new DataColumn("Address");
            userInfo.Columns.Add(Name);
            userInfo.Columns.Add(Age);
            userInfo.Columns.Add(Address);
            DataRow dr = userInfo.NewRow();
            dr["Name"] = "Sunny";
            dr["Age"] = 24;
            dr["Address"] = "a";
            userInfo.Rows.Add(dr);

            dr = userInfo.NewRow();
            dr["Name"] = "Cary";
            dr["Age"] = 25;
            dr["Address"] = "b";
            userInfo.Rows.Add(dr);    
            return userInfo;
        }

        public static IEnumerable<UserInfo> GetUserInfoByYield(DataTable dt)
        {
            if (dt != null)
            {
                UserInfo u = new UserInfo();
                foreach (DataRow aa in dt.Rows)
                {
                    u.Name = aa["Name"].ToString();
                    u.Address = aa["Address"].ToString();
                    u.Age = Convert.ToInt16(aa["Age"]);
                    yield return u;
                }
            }   
        }

        public static List<UserInfo> GetUserInfoByList(DataTable dt)
        {
            List<UserInfo> userInfo = new List<UserInfo>();
            foreach (DataRow u in dt.Rows)
            {
                UserInfo uu = new UserInfo();
                uu.Name = u["Name"].ToString();
                uu.Address = u["Address"].ToString();
                uu.Age = Convert.ToInt16(u["Age"]);
                userInfo.Add(uu);
            }
            return userInfo;

        }
    }
}