Enumerable in C#——内迭代与外迭代示例

昨晚家里上不了网，打开以前下的视频:what's new in csharp 3.0 ?.感叹于VS开发环境的中Code Snippet，以及 CSharp3.0 对迭代的支持。

随手仿照视频写了一个代码，用来演示CSharp3.0对迭代的支持。

  1using System;
  2using System.Collections.Generic;
  3using System.Linq;
  4using System.Text;
  5
  6namespace EnumerableTest
  7{
  8    class Customer
  9    {
 10        public string CustomerID { get; set; }
 11        public string ContactName { get; set; }
 12        public string City { get; set; }
 13    }
 14
 15
 16    class Program
 17    {
 18        static void Main(string[] args)
 19        {
 20            List<Customer> customers = LoadCustomers();
 21
 22            Outer Iteration#region Outer Iteration
 23            //使用外迭代 One
 24            foreach (var cust in customers)
 25            {
 26                PrintCustomer(cust);  //可将迭代子(Iterator)传给其它函数
 27
 28                //也可以进行Filter，但不是很Elegant
 29                if (cust.City == "Suzhou")
 30                    PrintCustomer(cust);
 31            }
 32            SeparatorLine();
 33            //使用外迭代 Two
 34            IEnumerator<Customer> itor = customers.GetEnumerator();
 35            while (itor.MoveNext())
 36            {
 37                PrintCustomer(itor.Current);
 38            }
 39            SeparatorLine();
 40            
 41            #endregion
 42
 43
 44            Inner Iteration#region Inner Iteration
 45            //使用内迭代，对每个元素执行一个操作(函数),思想上实现了函数式编程
 46            //语义上：对每个元素执行，一个函数Action（PrintCustomer）,下面的语义等同于：
 47            //Action<Customer> printCustomer = delegate(Customer c)
 48            //{
 49            //    Console.WriteLine("ID:{0} Contact:{1} City:{2}", c.CustomerID.PadRight(10), c.ContactName.PadRight(10), c.City);
 50            //};
 51            //customers.ForEach(printCustomer);
 52            customers.ForEach(c => PrintCustomer(c));  //More convenience, more elegant
 53            SeparatorLine();
 54
 55            //使用内迭代，进行Filter:Where(c => c.City == "Suzhou")
 56            customers.Where(c => c.City == "Suzhou").ToList().ForEach(c => PrintCustomer(c));
 57            SeparatorLine();
 58            //多级Filter
 59            customers.Where(c => c.City == "Suzhou").Where(c => c.ContactName == "Peter").ToList().ForEach(c => PrintCustomer(c));
 60            SeparatorLine(); 
 61            #endregion
 62
 63
 64            LINQ,对迭代的SQL Syntax式支持，我不太喜欢，还是感觉函数式编程更爽些，更直观些#region LINQ,对迭代的SQL Syntax式支持，我不太喜欢，还是感觉函数式编程更爽些，更直观些
 65            //似乎对于LINQ来说，Query功能完善。而：对于每一个元素执行一个操作（函数）却不支持.
 66            var result = from c in customers
 67                         where c.City == "Suzhou"
 68                         where c.ContactName == "Peter"
 69                         select c;
 70
 71            result.ToList().ForEach(c => PrintCustomer(c));
 72
 73            SeparatorLine();
 74            #endregion
 75
 76
 77            Console.ReadKey();
 78        }
 79
 80        private static void SeparatorLine()
 81        {
 82            Console.WriteLine();
 83        }
 84
 85        private static void PrintCustomer(Customer cust)
 86        {
 87            Console.WriteLine("ID:{0} Contact:{1} City:{2}", cust.CustomerID.PadRight(10), cust.ContactName.PadRight(10), cust.City);
 88        }
 89
 90        private static List<Customer> LoadCustomers()
 91        {
 92            List<Customer> customers = new List<Customer>() 
 93            { 
 94                new Customer(){ CustomerID="Andrew", ContactName="Anco", City="Hefei"},
 95                new Customer(){ CustomerID="Nortel", ContactName="Anco", City="Shanghai"},
 96                new Customer(){ CustomerID="Cisco", ContactName="Candy", City="Beijing"},
 97                new Customer(){ CustomerID="HP", ContactName="Peter", City="Suzhou"},
 98                new Customer(){ CustomerID="Lenovo", ContactName="Linda", City="Suzhou"}
 99            };
100            return customers;
101        }
102    }
103}
104