c# - 如何正确使用C# 8.0 switch case

Question

我尝试实现 c# 8.0 switch-case 但不幸的是它不起作用，我想如果满足 case 则在 switch 表达式中返回满足 case 的特定字符串。

这是我的代码:

public static void GetErrMsg(Exception ex) =>
   ex switch
   {
       ex is UserNotFoundException => "User is not found.",
       ex is NotAuthorizedException => "You'r not authorized."
   };

但我收到以下消息:

Error CS0201 Only assignment, call, increment, decrement, await, andnew object expressions can be used as a statement.

Error CS0029 Cannot implicitly convert type 'bool' to'System.Exception'

Answer 1

也许是这样的:

    public static string GetErrMsg(Exception ex) =>
       ex switch
       {
           UserNotFoundException _ => "User is not found.",
           NotAuthorizedException _ => "You'r[e] not authorized.",
           _ => ex.Message, // or something; "Unknown error" perhaps
       };

这里的_是废弃的；如果您确实想使用检测到的类型中的其他内容，您可以为其命名，例如:

UserNotFoundException unfe => $"User is not found: {unfe.UserName}",