Question

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

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