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Subject: Re: [boost] Need for BOOST_PP_VARIADIC_POP_FRONT
From: Edward Diener (eldiener_at_[hidden])
Date: 2011-11-13 13:22:43

On 11/13/2011 12:47 PM, Gennadiy Rozental wrote:
> Edward Diener<eldiener<at>> writes:
>> On 11/13/2011 11:05 AM, Gennadiy Rozental wrote:
>>> Paul Mensonides<pmenso57<at>> writes:
>>>> Variadic data is not a true data structure and should not be supported as
>>>> such. Therefore, it should not have a POP_FRONT, for example. Convert it
>>>> into a real data structure (such as a sequence) and then do your
>>>> processing on that data structure.
>>> How would it help me if I want to take first arguments from __VA_ARGS__
>>> and pass the rest to the different variadic macro?
>> First I would say that it would be better internally to pass a PP
>> sequence to your different macro rather than variadic data.
> And what if the second macro is part of public interface as well?

Then use another macro internally that uses PP tuples, seqs, or lists.

>> But if you want to do it the way you say above, just convert the
>> variadic data to a PP sequnce using BOOST_PP_VARIADIC_TO_SEQ, pop the
>> first element from the sequence using BOOST_PP_SEQ_POP_FRONT, convert
>> the sequence back to variadic data using BOOST_PP_SEQ_ENUM, and pass
>> that data as your variadic data.
> That's good. Why not wrap it all into a simple macro that does it all?

Because I would only be duplicating endless functionality which the
other Boost PP data types already have.

>> In my VMD library and the work I did with Paul in adding variadic data
>> to the preprocessor code on the trunk, I always mentioned that I viewed
>> C++ variadic data as an easier to use interface for end-users but that
>> Boost PP has much richer data types internally.
> That's the core issue: variadic data provides better interface. And do not see
> why we should discourage use of it. I believe it should be supported completely
> with all the necessary interfaces. Internally we should be free to convert back
> and forth between variadic data and PP data structures, but it's implementation
> detail.

I agree that it provides an easier to use interface for the end user.
But I strongly disagree that it is a better interface than the other
Boost PP data types.


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