C#中Lambda表达式的三种写法

一、历史版本

delegate void StudentDelegate(string name, int age);
public class LambdaTest
{
    public void Show()
    {
        DateTime dateTime = DateTime.Now;
        //历史
        //版本1
        {
            StudentDelegate student = new StudentDelegate(PrintStudent);
            student("葛优", 1);
        }
    }
}

public void PrintStudent(string name,int age)
{
    Console.WriteLine($"我的名字是：{name},我的年龄是{age}");
}

二、版本二:访问局部变量

delegate void StudentDelegate(string name, int age);
public class LambdaTest
{
    public void Show()
    {
        DateTime dateTime = DateTime.Now;
        //版本2(这样写的话可以访问局部变量)
        {
            StudentDelegate student = new StudentDelegate( delegate (string name, int age)
            {
                Console.Write(dateTime);
                Console.WriteLine($"我的名字是：{name},我的年龄是{age}");
            });
            student("王朝伟", 1);
        }
    }
}

三、版本三: “=>”

delegate void StudentDelegate(string name, int age);
public class LambdaTest
{
    public void Show()
    {
        DateTime dateTime = DateTime.Now;
        //版本3(=>念成gose to)
        {
            StudentDelegate student = new StudentDelegate((string name, int age)=>
            {
                Console.Write(dateTime);
                Console.WriteLine($"我的名字是：{name},我的年龄是{age}");
            });
            student("刘德华", 1);
        }
        {
            Action action = () => Console.WriteLine("无返回值，无参数");
            Action<DateTime> action1 = d => { Console.WriteLine( $"带一个参数：{d}"); };
            action1(dateTime);

            Action<DateTime, int> action2 = (d, i) => { Console.WriteLine(  $"带两个参数：{ d} ,{ i}"); };
            action2(dateTime, 3);

            Func<DateTime> func=()=>{ return DateTime.Now; };//带返回值
            DateTime dateTime1 = func();//调用Lambda获取值 
            Console.WriteLine(dateTime1);

            Func<DateTime> func2 = () => DateTime.Now;//带返回值
            Console.WriteLine(func2());
        }
    }
}

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