lambda表达式一

lambda表达式1
Lambda表达式

Sample 1

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace ConsoleApplication1{    public delegate int mydg(int a,int b);    public static class LambdaTest    {        public static int oper(this int a, int b, mydg dg)        {            return dg(a, b);        }    }    class Program    {        static void Main(string[] args)        {            Console.WriteLine(1.oper(2, (a, b) => a + b));            Console.WriteLine(2.oper(1, (a, b) => a - b));            Console.ReadLine();        }    }}

运行结果：

31

分析：
1、    public delegate int mydg(int a, int b);
非常重要，代理，Lambda表达式就是delegate
2、 public static int oper(this int a, int b, mydg dg)
静态方法，结合this的使用，可以通过这种方式对已有类添加方法。
不过这里添加的方法是Lambda表达式。
3、1.oper(2, (a, b) => a + b)
实际执行的是LambdaTest.oper(1,2,(a,b)=>a+b);
补充，所有的类的方法基本上都是用这种方式来执行的。


Sample 2

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace ConsoleApplication1{    public class Person    {        public string username { get; set; }        public int age { get; set; }        public override string ToString()        {            return string.Format("username:{0} age:{1}", this.username, this.age);        }    }    class Program    {        static void Main(string[] args)        {            var persons = new List<Person> {    new Person {username = "a", age=19},     new Person {username = "b", age=20},    new Person {username = "c", age=21},     };            var selectPerson = from p in persons where p.age >= 20 select p.username.ToUpper();            foreach (var p in selectPerson)                Console.WriteLine(p);            Console.ReadLine();        }    }}

分析：
  var selectPerson = from p in persons where p.age >= 20 select p.username.ToUpper();
等价于：
var selectPerson = persons.Where(p => p.age >= 20).Select(p => p.username.ToUpper());  


2011-6-2 10:17 danny

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