使用switch表达式简化switch语句

using System;
using System.IO;
                
public class Program
{
    public static void Main()
    {
        string path = @"C:\Users\user\Downloads";
        Console.Write("Press R for readonly or W for write:");
        ConsoleKeyInfo key = Console.ReadKey();
        Console.WriteLine();
        
        Stream s = null;
        if(key.Key == ConsoleKey.R)
        {
            s = File.Open(
            Path.Combine(path,"file.txt"),
            FileMode.OpenOrCreate,
            FileAccess.Read);
        }
        else
        {
            s = File.Open(
            Path.Combine(path,"file.txt"),
            FileMode.OpenOrCreate,
            FileAccess.Write);
        }
        
        //以往写法
        string message = string.Empty;
        switch(s)
        {
            case FileStream writeableFile when s.CanWrite:
                message = "The stream is a file that I can write to.";
                break;
            case FileStream readOnlyFile:
                message = "The stream is a read-only file.";
                break;
            case MemoryStream ms:
                message = "The stream is a memory address.";
                break;
            default:
                message = "The stream is some other type.";
                break;
            case null:
                message = "The stream is null";
                break;
        }
        
        //C#8.0以上switch表达式简化switch语句
        message = s switch
        {
            FileStream writeableFile when s.CanWrite
                =>"The stream is a file that I can write to.",
            FileStream readOnlyFile
                =>"The stream is a read-only file.",
            MemoryStream ms
                =>"The stream is a memory address.",
            null
                =>"The stream is null",
            _
                =>"The stream is some other type."
        };
        Console.WriteLine(message);
        
    }
}