1 using System;
2 using System.IO;
3
4 public class Program
5 {
6 public static void Main()
7 {
8 string path = @"C:\Users\user\Downloads";
9 Console.Write("Press R for readonly or W for write:");
10 ConsoleKeyInfo key = Console.ReadKey();
11 Console.WriteLine();
12
13 Stream s = null;
14 if(key.Key == ConsoleKey.R)
15 {
16 s = File.Open(
17 Path.Combine(path,"file.txt"),
18 FileMode.OpenOrCreate,
19 FileAccess.Read);
20 }
21 else
22 {
23 s = File.Open(
24 Path.Combine(path,"file.txt"),
25 FileMode.OpenOrCreate,
26 FileAccess.Write);
27 }
28
29 //以往写法
30 string message = string.Empty;
31 switch(s)
32 {
33 case FileStream writeableFile when s.CanWrite:
34 message = "The stream is a file that I can write to.";
35 break;
36 case FileStream readOnlyFile:
37 message = "The stream is a read-only file.";
38 break;
39 case MemoryStream ms:
40 message = "The stream is a memory address.";
41 break;
42 default:
43 message = "The stream is some other type.";
44 break;
45 case null:
46 message = "The stream is null";
47 break;
48 }
49
50 //C#8.0以上switch表达式简化switch语句
51 message = s switch
52 {
53 FileStream writeableFile when s.CanWrite
54 =>"The stream is a file that I can write to.",
55 FileStream readOnlyFile
56 =>"The stream is a read-only file.",
57 MemoryStream ms
58 =>"The stream is a memory address.",
59 null
60 =>"The stream is null",
61 _
62 =>"The stream is some other type."
63 };
64 Console.WriteLine(message);
65
66 }
67 }
