Re: [boost] Enums: naming question?

Subject: Re: [boost] Enums: naming question?
From: Vicente Botet (vicente.botet_at_[hidden])
Date: 2011-03-19 07:20:29

Jeffrey Lee Hellrung, Jr.-2 wrote:
> 
> On Sat, Mar 19, 2011 at 1:10 AM, Vicente Botet
> <vicente.botet_at_[hidden]>wrote:
> 
>>
>> Jeffrey Lee Hellrung, Jr.-2 wrote:
> 
>> > So what's with scoping_type?  In one case, it's the scoped enum, and in
>> > the other case, it's the emulated scoped enum, but in both it looks
>> like
>> > an
>> > identity operation.  I don't get the point.
>> >
>>
>> It is not the identity when the scoped enum is emulated. In any case is
>> the
>> type giving scope to the enumerators, this was the reason for the name.
>>
>> In the emulation scoping of the nested enum is the identity.
> 
> 
> This seems to contradict your earlier statement: "It is not the identity
> when the scoped enum is emulated."  Can you elaborate?  Do you mean that
> the
> scoping_type maps the "native enum" type of the (emulated) scoped enum
> back
> to the (emulated) scoped enum?  I.e., native_type and scoping_type are
> inverse metafunctions?
> 

Yes.

>> With scoped
>> enums scoping and enum_type/native_type are identities.
>>
>> I'm conscientious  that this alternative emulation of enums has a major
>> drawback: the emulating type is not an enum and I can understand why
>> others
>> have abandoned the idea. I just wanted to explore it in depth to see if
>> the
>> whole design had more advantages than liabilities, but I suspect that
>> I've
>> not reached it yet.
> 
> 
> Actually, what I've seen of the design so far seems very reasonable.  I
> will
> try to take a closer look at the documentation to get a better sense of
> the
> limitations of the emulation.
> 
> I guess the thing I'd be worried about is how necessary or in-demand
> scoped
> enums are.  There are clear benefits to them, as evident by their
> inclusion
> in the standard, but emulating it doesn't seem like such a big deal as,
> for
> example, the move/rvalue reference emulation that Boost.Move provides.
> 

I agree partially. I'm concerned by the scoped enums that are already
defined by the standard C++ and that have an equivalent on Boost. Without an
emulation there is no way to write portable programs that can adapt to the
whether the scoped enum is supported by the compiler.

Beman has created his scoped enum emulation just for this purpose, but it
lacks some scoped enum features as it is implicitly convertible to the
underlying type.

> As the emulation is not an enum we need some traits to
>> get the enum type and vice versa. The same is applicable for the value
>> conversion of these type.
>>
> 
> Sure, makes sense.
> 

Thanks for your interest,
Vicente

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