enum

[Andrei Alexandrescu]

On 4/12/14, 5:59 AM, Jonathan M Davis wrote:
> On Friday, April 11, 2014 19:52:58 Andrei Alexandrescu wrote:
>> On 4/11/14, 6:59 PM, Jonathan M Davis wrote:
>>> On Friday, April 11, 2014 17:01:15 Andrei Alexandrescu wrote:
>>>> On 4/11/14, 12:31 PM, Jonathan M Davis wrote:
>>>>> On Friday, April 11, 2014 08:22:01 Steven Schveighoffer wrote:
>>>>>> final enum name { ... }
>>>>>
>>>>> This only makes sense to me if it's then illegal to declare any
>>>>> variables
>>>>> of that enum type, because if you're looking to use an enum to give a
>>>>> list of possible values rather than enumerating the exact list of
>>>>> values,
>>>>> why would you be marking _any_ variable as being of that enum type?
>>>>
>>>> I don't understand that contention. "final" clarifies that the set of
>>>> values in the enumeration is closed.
>>>
>>> I take issue with the idea that it makes sense to have any variables of an
>>> enum type that isn't one of the values enumerated in the enum.
>>
>> I explained the possible situations in the original post of this thread.
>> E.g. one may be unable to enumerate all user IDs, but may be compelled
>> to enumerate a few remarkable ones and ascribe user IDs a separate type.
>> -- Andrei
>
> And what would the purpose by of giving them their own type?

Less error proneness.

> If the enum
> doesn't enumerate all of the values, then you're clearly going to be using
> other values with it, meaning that any restrictions on setting a variable to
> those other values is going to be a problem (as is currently the case with
> enums - assignment and initialization are protected against non-enumerated
> values). You'd just end up with a enum type which is effectively an alias for
> the enum's base type except that assigning it non-enumerated values requires
> casting, and you can overload a function on the enumerated values vs the non-
> enumerated ones (or at  least, non-enumerated ones which aren't cast to the
> enum type) by overloading a function on the enum type and its base type -
> which would be highly bug-prone IMHO.

Sorry, your speculations are mistaken. The pattern works well and we've 
been using it repeatedly and with good results since C++ introduced 
"enum class".


Andrei