Lambda表达式

1. lambda表达式是一个匿名函数，匿名方法。

namespace lambda
{
    public delegate void NoReturnWithPara(string name); //声明委托
    class LambdaShow
    {
        public void Show()
        {

            {
                NoReturnWithPara method = new NoReturnWithPara(this.Study);   //声明委托实例，调用方法
                method.Invoke("YOYO");
            }

            {
                NoReturnWithPara method = new NoReturnWithPara(     //单独声明的方法换成匿名方法
                    delegate (string name)
                    {
                        Console.WriteLine("{0} is studying lambda !", name);
                    }
                 );
            }

            {
                NoReturnWithPara method = new NoReturnWithPara(     //单独声明的方法换成匿名方法
                  (string name) =>//delegate关键字换成了goes to =>
                  {
                        Console.WriteLine("{0} is studying lambda !", name);
                  }
                 );
            }

            {
                NoReturnWithPara method = new NoReturnWithPara(     //单独声明的方法换成匿名方法
                  (name) =>//委托实例化要求方法的签名必须和委托一致
                  {
                      Console.WriteLine("{0} is studying lambda !", name);
                  }
                 );
            }

            {
                NoReturnWithPara method = new NoReturnWithPara(     //单独声明的方法换成匿名方法
                  name=>//只有一个参数可以去掉小括号；如果方法体只有一行，大括号和分号也都可以去掉  
                      Console.WriteLine("{0} is studying lambda !", name)
                 );
            }

            {
                //委托实例化可以不要new
                NoReturnWithPara method = name => Console.WriteLine("{0} is studying lambda !", name);
             }
          
        }
        private void Study(string name)
        {
            Console.WriteLine("{0} is studying lambda !", name);
        }
    }
}

2. .net提供了两个标准的委托  Action 和 Func

//.net提供了两个标准的委托

            // public delegate void Action(); 无参数无返回值
            Action act1 = () => Console.WriteLine("test");

            //public delegate void Action<in T>(T obj); 有参数无返回值的泛型委托
            Action<string> act2 = name => Console.WriteLine("test");
            Action <int,string > act4=(id,name) => Console.WriteLine("test");

            //0个泛型参数，无返回值的委托
            Action<string, int, double, DateTime, long, decimal, float, string, int, double, DateTime, long, decimal, float, decimal, float> act3 = null;

            // public delegate TResult Func<out TResult>(); 无参数有一个返回值的委托
            //里面的in,out代表输入参数，输出结果
            //这里不需要return，直接给返回值
            Func<int> fun1 = () => 3;

            // 一个参数一个返回值的委托
            Func<string, int> fun2 = s => 3;

            //两个参数一个返回值的委托
            Func<string, int, int> fun3 = (s, i) => 3;

            //16个参数一个返回值的委托
            Func<string , string, int, double, DateTime, long, decimal, float, string, int, double, DateTime, long, decimal, float, decimal, float> fun4 = null;
            

3. linq扩展展示

    class LinqShow
    {
        public static void Show()
        {
            List<int> intList = new List<int>()
           { 21,56,95,234,854,12,456};

            //Func<int, bool> func = t => t > 100;
            foreach (var item in intList .Where(t=>t>100)) //陈述式的语法
            {
                Console.WriteLine(item);
            }

            foreach (var item in intList.Where(t => t > 100)
                .Select(t=>string .Format ("这里是数字{0}",t))
                .OrderBy(t=>t)) 
            {
                Console.WriteLine(item);
            }
        }
    }