private void Func(string msg)
 {
 if (string.IsNullOrEmpty(msg))
 {
 throw new ArgumentException(nameof(msg));
 }
 }

using System;
using SystemTest = System.Text;
namespace _01_nameof
{
 class Program
 {
 private static void Func1(int x) { }
 private string F<T>() => nameof(T);
 private void Func2(string msg) { }
 static void Main(string[] args)
 {
 var program = new Program();
 Console.WriteLine(nameof(SystemTest));
 Console.WriteLine(nameof(Func1));
 Console.WriteLine(nameof(Program));
 Console.WriteLine(nameof(program));
 Console.WriteLine(nameof(F));
 Console.Read();
 }
 }
}

 var name = "Fanguzai";
 Console.WriteLine($"Hello, {name}");

 var s1 = $"hello, {name}";
 IFormattable s2 = $"Hello, {name}";
 FormattableString s3 = $"Hello, {name}";

string name = null; 
 Console.WriteLine($"1：{name?.Length}");
 name = "Fanguzai";
 Console.WriteLine($"2：{name?.Length}");
 Console.WriteLine($"3: {name?[0]}");

//普通的委托调用
 Func<int> func = () => 0;
 if (func!=null)
 {
 func();
 }
 //简化调用
 func?.Invoke();

async Task Test()
 {
 var wc = new WebClient();
 try
 {
 await wc.DownloadDataTaskAsync("");
 }
 catch (Exception)
 {
 await wc.DownloadDataTaskAsync("");　　//OK
 }
 finally
 {
 await wc.DownloadDataTaskAsync("");　　//OK
 }
 }

class MyClass
 {
 public string Name { get; set; } = "Fanguzai";
 }
 static void Main(string[] args)
 {
 var myClass=new MyClass();
 Console.WriteLine(myClass.Name);
 Console.Read();
 }

class MyClass
 {
 public string Name { get; set; }
 public MyClass()
 {
 Name = "Fanguzai";
 }
 }

class Person
 {
 //新语法
 private string Name { get; } = "Fanguzai"; //不用带上 private set;
 //旧语法
 public int Age { get; private set; } ;
 }

class MyClass
 {
 public int this[int id] => id; //索引
 public double Add(int x, int y) => x + y; //带返回值方法
 public void Output() => Console.WriteLine("Hi, Fanguzai!"); //无返回值方法
 }

var nums = new Dictionary<int, string>
 {
 [7] = "seven",
 [9] = "nine",
 [13] = "thirteen"
 };
 //这是旧的方式
 var otherNums = new Dictionary<int, string>()
 {
 {1, "one"},
 {2, "two"},
 {3, "three"}
 };

using System;
using static System.Console;
namespace _08_usingStatic类型
{
 class Program
 {
 static void Main(string[] args)
 {
 Console.WriteLine("Hi,Fanguzai!");
 WriteLine("Hi,Fanguzai!"); // 使用了 using static System.Console;
 }
 }
}