Re: [boost] [preprocessor] [variadic] BOOST_PP_VARIADICS vs BOOST_NO_VARIADIC_MACROS

Subject: Re: [boost] [preprocessor] [variadic] BOOST_PP_VARIADICS vs BOOST_NO_VARIADIC_MACROS
From: Lorenzo Caminiti (lorcaminiti_at_[hidden])
Date: 2012-01-14 05:42:10

On Sun, Dec 18, 2011 at 10:18 AM, Paul Mensonides <pmenso57_at_[hidden]> wrote:
> On Sat, 17 Dec 2011 12:45:26 -0800, lcaminiti wrote:
>> Why does Boost.Preprocessor redefines BOOST_PP_VARIAIDCS instead of just
>> using BOOST_NO_VARIADIC_MACROS from Boost.Config?
>
> The pp-lib requires more than just superficial variadic macro support.
> I.e. BOOST_PP_VARIADICS macro is stronger.
>
>> Furthermore, GCC supports variadics also when C++11 extensions are not
>> enabled so I think the following should not &&
>> __GXX_EXPERIMENTAL_CXX0X__:
>>
>> // File: boost/preprocessor/config/config.hpp #    /* Wave (C/C++), GCC
>> (C++) */
>> #    elif defined __WAVE__ && __WAVE_HAS_VARIADICS__ || defined __GNUC__
>> && __GXX_EXPERIMENTAL_CXX0X__
>> #        define BOOST_PP_VARIADICS 1
>
> Because it isn't standard C++98.  It can be enabled via a command line
> definition of BOOST_PP_VARIADICS.  It is enabled by default (on GCC) when
> in C++11 mode.  I believe that GCC 4.7 actually finally defines __cplusplus
> correctly as well.

It is annoying to manually -DBOOST_PP_VARIADICS. That is especially
true for libraries like Boost.ScopeExit and Boost.Closure that use
variadics in their public APIs so the end user is required to manually
define BOOST_PP_VARIADICS when Boost.Preprocessor does not
automatically detect it... (e.g., on GCC 4.5.3 without -std=c++0x).

Can we define what "extra" features are required by BOOST_PP_VARIADICS
so I can write tests and run them to the Boost compilers and then
refine the definition of BOOST_PP_VARIADICS to automatically detect
all compilers where Boost.Preprocessor variadic support work.

Thanks a lot.
--Lorenzo