五、Lambda和Linq

1.Lambda的演变历史

public delegate void NoReturnNoPara();
public delegate void NoReturnWithPara(int x, string y);
public delegate int WithReturnNoPara();
public delegate string WithReturnWithPara(out int x, ref int y);
public void ShowLambdaHistory()
{
   
    Console.WriteLine($"在.NetFramework1.0/1.1时代");
    NoReturnNoPara method1 = new NoReturnNoPara(DoNothing);
    method1.Invoke();
    NoReturnWithPara method2 = new NoReturnWithPara(Study);
    method2.Invoke(3, "牧舟");
    Console.WriteLine();

    Console.WriteLine("在.NetFramework2.0时代 —— 匿名方法");
    Console.WriteLine("增加了一个delegate关键字，可以访问到除了参数以外的局部变量");
    string localVar = "局部变量";
    NoReturnWithPara method3 = new NoReturnWithPara(delegate (int id, string name)
    {
   
        Console.WriteLine($"参数：{
     id}，{
     name}学习高级班课程，   localVar = {
     localVar}");
    });
    method3.Invoke(10, "牧舟");
    Console.WriteLine();

    Console.WriteLine("在.NetFramework3.0时代");
    Console.WriteLine("去掉了delegate关键字，添加了一个符号=>，读作“goes to”");
    NoReturnWithPara method4 = new NoReturnWithPara((int id, string name) =>
    {
   
        Console.WriteLine($"参数：{
     id}，{
     name}学习高级班课程，   localVar = {
     localVar}");
    });
    method4.Invoke(11, "牧舟");
    Console.WriteLine();

    Console.WriteLine("在.NetFramework3.0时代后期");
    Console.WriteLine("去掉了匿名方法中的参数类型，编译器自动推断(语法糖)");
    NoReturnWithPara method5 = new NoReturnWithPara((id, name) =>
    {
   
        Console.WriteLine($"参数：{
     id}，{
     name}学习高级班课程，   localVar = {
     localVar}");
    });
    method5.Invoke(13, "牧舟");
    Console.WriteLine();

    Console.WriteLine("如果匿名方法体中，只有一行代码，可以省略方法体的大括号");
    NoReturnWithPara method6 = new NoReturnWithPara((id, name) => 
    Console.WriteLine($"参数：{
     id}，{
     name}学习高级班课程，   localVar = {
     localVar}"));
    method6.Invoke(14, "牧舟");
    Console.WriteLine("继续精进……");
    NoReturnWithPara method7 = (id, name) =>
    Console.