Correct exception to throw for an unhandled switch case for an argument?

Question

NOTE: This is different than the proposed duplicates as this deals with an argument rather than a value. The behavior and applicable scenarios are essentially different.

Say we have SomeEnum and have a switch statement handling it like:

enum SomeEnum
{
    One,
    Two,
}

void someFunc(SomeEnum value)
{
    switch(value)
    {
        case SomeEnum.One:
            ...
            break;
        case SomeEnum.Two:
            ... 
            break;
        default:
            throw new ??????Exception("Unhandled value: " + value.ToString());    
    }
}

As you see we handle all possible enum values but still keep a default throwing an exception in case a new member gets added and we want to make sure we are aware of the missing handling.

My question is: what's the right exception in such circumstances where you want to notify that the given code path is not handled/implemented or should have never been visited? We used to use NotImplementedException but it doesn't seem to be the right fit. Our next candidate is InvalidOperationException but the term doesn't sound right. What's the right one and why?

EDIT: C# 8.0 introduced switch expressions which produce compiler warnings for non-exahustive switch statements. That's another reason why you should use switch expressions over switch statements whenever applicable. The same function can be written in a safer way like:

void someFunc(SomeEnum value)
{
    _ = value switch
    {
        SomeEnum.One => ....,
        SomeEnum.Two => ...., 
    }
}

When a new member gets added to SomeEnum, the compiler will show the warning "CS8509: The switch expression does not handle all possible values of its input type (it is not exhaustive). For example, the pattern 'EnumHandling.SomeEnum.Three' is not covered." for the switch expression which makes it way easier to catch potential bugs.

Answer 1

ArgumentException looks the most correct to me in this instance (though is not defined in the BCL).

There is a specialized exception for enum arguments - InvalidEnumArgumentException:

The exception thrown when using invalid arguments that are enumerators.

An alternative is ArgumentOutOfRangeException:

The exception that is thrown when the value of an argument is outside the allowable range of values as defined by the invoked method.

The logic for using these is that the passed in argument (value) is not valid as far as someFunc is concerned.

Answer 2

I'd throw the InvalidEnumArgumentException as it will give more detailed information in this case, you are checking on an enum

Answer 3

Since you have the login in a function you can throw InvalidArgumentException.

The exception that is raised when a parameter that is not valid is passed to a method on the referenced connection to the server.

EDIT: A better alternative would be: ArgumentException, since InvalidArgumentException in Microsoft.SqlServer.Management.Common namespace. Something like:

throw new ArgumentException("Unhandled value: " + value.ToString());

Answer 4

InvalidArgumentException. when user pass some invalid value or null value when value value is required, it is recommended to handle InvalidArgumentException .

Answer 5

If you were using Code Contracts (something I HIGHLY recommend), you would put this at the start of the method:

Contract.Requires(value == SomeEnum.One || value == SomeEnum.Two);

If you want to check a range of an enum which has too many individual values to write them all explicitly, you can do it like this:

Contract.Requires(SomeEnum.One <= value && value <= SomeEnum.Two);