为LINQ服务的C#新特性总结篇---扩展方法，匿名委托，lambda表达式，Action委托，Func委托，Linq中的order by,top和sum函数

更新时间：2021-09-26 14:19:16

Code
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using System.Diagnostics;

namespace ConsoleApplication1
{
    static class Program
    {
        static void Main(string[] args)
        {
            //Predicate
            //把方法当作参数传递
            DisplayProcess(Filter);
            //匿名委托
            DisplayProcess(delegate(Process process) { return process.WorkingSet64 >= 20 * 1024 * 1024; });
            //lambda表达式
            DisplayProcess(process =>  process.WorkingSet64 >= 20 * 1024 * 1024);

            //action
            Action<string> print_string = (s) =>  Console.WriteLine(s);
            print_string.Invoke("就这么简单!");
            //Func
            Func<DateTime> get_time = () => DateTime.Now;
            DateTime now = get_time.Invoke();
            print_string.Invoke(now.ToString());
            //扩展方法
            List<int> int_list = new List<int> { 1, 2, 3, 4, 5, 6, 7 };
            int b= int_list.list_sum();
            print_string.Invoke(b.ToString());
            //sql中的top和order by
            var c = int_list.OrderByDescending(i => i).Take(3);
            foreach (int k in c)
            {
                print_string.Invoke(k.ToString());
            }
            var d = int_list.OrderByDescending(i => i).Take(3).Sum();
            print_string.Invoke(d.ToString());

            Console.ReadKey();
        }
        /// <summary>
        /// 扩展方法必须在非泛型静态类中定义
        /// </summary>
        /// <param name="list"></param>
        /// <returns></returns>
        static int list_sum(this IEnumerable<int> list)
        {
            int a = 0;
            foreach (var i in list)
            {
                a += i;
            }
            return a;
        }
        /// <summary>
        /// Predicate<Process>是泛型委托
        /// 定义如下public delegate bool Predicate<T>(T obj);
        /// </summary>
        /// <param name="match"></param>
        private static void DisplayProcess(Predicate<Process> match)
        {
            foreach(var process in Process.GetProcesses())
            {
                if (match(process))
                {
                    Console.WriteLine("{0}            {1}", process.ProcessName, process.WorkingSet64);
                }
            }

        }
        private static bool Filter(Process process)
        {
            return process.WorkingSet64 >= 20 * 1024 * 1024;
        }
    }
}

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为LINQ服务的C#新特性总结篇---扩展方法，匿名委托，lambda表达式，Action委托，Func委托，Linq中的order by,top和sum函数

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