扔在switch语句中的异常时，没有指定的情况下，可以处理 [英] Throwing exceptions in switch statements when no specified case can be handled

问题描述

我已经写C＃在过去的8年，已经变得相当的防守OOP编程。在静态类型语言工作，你不喜欢的东西验证参数的方法，并抛出异常，你就不会在是动态的，更自由的语言。我认为自己在C＃中的专家，并正在寻找从最佳做法的其他精通C＃开发人员的反馈意见。

I've been writing C# for the last 8 years and have become quite the defensive OOP programmer. Working in a statically-typed language, you do things like validate arguments in methods and throw exceptions where you wouldn't in languages that are dynamic and more liberal. I consider myself an expert in C# and am looking for feedback from other well-versed C# developers on best practices.

让我们说我们有，对于更改密码功能用户在一个MVC应用程序的系统：

Let's say we have a function that changes a password for a user in a system in an MVC app.:

public JsonResult ChangePassword
    (string username, string currentPassword, string newPassword)
{
    switch (this.membershipService.ValidateLogin(username, currentPassword))
    {
        case UserValidationResult.BasUsername:
        case UserValidationResult.BadPassword:
            // abort: return JsonResult with localized error message        
            // for invalid username/pass combo.
        case UserValidationResult.TrialExpired
            // abort: return JsonResult with localized error message
            // that user cannot login because their trial period has expired
        case UserValidationResult.Success:
            break;
    }

    // NOW change password now that user is validated
}

membershipService.ValidateLogin（）返回定义为 UserValidationResult 枚举：

enum UserValidationResult
{
    BadUsername,
    BadPassword,
    TrialExpired,
    Success
}

作为一个防御性的程序员，我会改变上述的ChangePassword（）方法抛出一个异常，如果有从 UserValidationResult 值回> ValidateLogin（）：

Being a defensive programmer, I would change the above ChangePassword() method to throw an exception if there's an unrecognized UserValidationResult value back from ValidateLogin():

public JsonResult ChangePassword
    (string username, string currentPassword, string newPassword)
{
    switch (this.membershipService.ValidateLogin(username, currentPassword))
    {
        case UserValidationResult.BasUsername:
        case UserValidationResult.BadPassword:
            // abort: return JsonResult with localized error message        
            // for invalid username/pass combo.
        case UserValidationResult.TrialExpired
            // abort: return JsonResult with localized error message
            // that user cannot login because their trial period has expired
        case UserValidationResult.Success:
            break;
        default:
            throw new NotImplementedException
                ("Unrecognized UserValidationResult value.");
            // or NotSupportedException()
            break;
    }

    // Change password now that user is validated
}

我一直认为像上面一个最佳实践的最后一个片段的模式。例如，如果什么人开发得到，现在当用户尝试登录的要求，如果此有或业务原因，他们想先联系业务？因此， UserValidationResult 的定义更新为：

I always considered a pattern like the last snippet above a best practice. For example, what if one developer gets a requirement that now when users try to login, if for this-or-that business reason, they're suppose to contact the business first? So UserValidationResult's definition is updated to be:

enum UserValidationResult
{
    BadUsername,
    BadPassword,
    TrialExpired,
    ContactUs,
    Success
}

开发商改变了 ValidateLogin（）方法的主体返回新枚举值（ UserValidationResult.ContactUs ）的时候适用，但忘记更新的ChangePassword（）。如果没有开关外，用户仍然允许改变时，他们的登录尝试甚至不应该在第一时间确认自己的密码！

The developer changes the body of the ValidateLogin() method to return the new enum value (UserValidationResult.ContactUs) when applicable, but forgets to update ChangePassword(). Without the exception in the switch, the user is still allowed to change their password when their login attempt shouldn't even be validated in the first place!

难道只是我，或者是这个默认：抛出新的异常（）一个好主意？我看到它在几年前，始终认为这是一个最佳实践（groking后）。

Is it just me, or is this default: throw new Exception() a good idea? I saw it some years ago and always (after groking it) assume it to be a best practice.

推荐答案

我总是抛出例外在这种情况下。请考虑使用 InvalidEnumArgumentException ，这使在这种情况下，更丰富的信息。

I always throw an exception in this case. Consider using InvalidEnumArgumentException, which gives richer information in this situation.

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