Re: [Boost-users] [preprocessor] Undeclared identifier BOOST_PP_IIF_0 under Clang only

Subject: Re: [Boost-users] [preprocessor] Undeclared identifier BOOST_PP_IIF_0 under Clang only
From: Pierre Talbot (ptalbot_at_[hidden])
Date: 2014-04-03 17:16:17

On 04/03/2014 10:39 PM, Edward Diener wrote:
> On 4/3/2014 3:38 PM, Pierre Talbot wrote:
>> On 04/03/2014 05:31 PM, Edward Diener wrote:
>>> On 4/2/2014 3:48 PM, Pierre Talbot wrote:
>>>> Hi,
>>>>
>>>> I defined a macro using Boost.Preprocessor that compiles and works 
>>>> fine
>>>> under gcc but fails to compile under Clang. The macro is defined here:
>>>> https://github.com/ptal/Boost.Expected/blob/master/include/boost/functional/do_yield.hpp 
>>>>
>>>>
>>>
>>> As a quick shot, without actual testing, define BOOST_PP_VARIADICS 
>>> to 1.
>> It worked, thanks, but the problem is that it won't work if the user has
>> previously included preprocessor without having defined this macro.
>
> Agreed for any given translation unit which includes any of your headers.
>
> I would just explain to end-users of your library using Boost 1.55 or 
> lower that they need to define BOOST_PP_VARIADICS to 1 if they are 
> using clang and Boost PP. And/or you could also add to your library ( 
> in maybe a setup.hpp header ) something like:
>
> #if defined(BOOST_PP_VARIADICS)
> #if !BOOST_PP_VARIADICS
> #error BOOST_PP_VARIADICS cannot be defined as 0 when using Expected
> #endif
> #else
> #define BOOST_PP_VARIADICS 1
> #endif
Ok, this is a library intented to end in Boost so it won't be a problem 
if the issue is resolved in the last PP version. I'll use your solution 
meanwhile.
>
>> Maybe it should be defined by default if the language version is C++11?
>
> In the latest modular-boost BOOST_PP_VARIADICS is defined as 1 for all 
> versions of clang in the Boost PP config.hpp header. This was a 
> conservative oversight regarding clang by Paul Mensonides when 
> variadic macro support was added to pplib. I have since confirmed with 
> clang developers that clang always supported variadic macros even in 
> their earliest implementations and even without C++11 support.
Thanks for the insight!

Pierre
>
>>>
>>>>
>>>>
>>>> And the error message follows this message, the file using the 
>>>> macro is
>>>> https://github.com/ptal/Boost.Expected/blob/master/example/monadic_calculator/monadic_calculator.cpp 
>>>>
>>>>
>>>>
>>>>
>>>> Thanks for any helps,
>>>> Pierre Talbot
>>>>
>>>> Boost.Expected/example/monadic_calculator$ b2
>>>> ...patience...
>>>> ...found 1246 targets...
>>>> ...updating 2 targets...
>>>> clang-linux.compile.c++.without-pth
>>>> bin/clang-linux-3.5.0/debug/monadic_calculator.o
>>>> monadic_calculator.cpp:141:15: error: use of undeclared identifier
>>>> 'BOOST_PP_IIF_0'
>>>>      etokens = DO(
>>>>                ^
>>>> ../../include/boost/functional/do_yield.hpp:100:17: note: expanded 
>>>> from
>>>> macro 'DO'
>>>> #define DO(...) DO_SEQ(BOOST_PP_VARIADIC_TO_SEQ(__VA_ARGS__))
>>>>                  ^
>>>> ../../include/boost/functional/do_yield.hpp:97:3: note: expanded from
>>>> macro 'DO_SEQ'
>>>>    BOOST_PP_SEQ_FOR_EACH_I(DO_ELEM, seq, seq) \
>>>>    ^
>>>> /usr/local/boost_1_55_0/boost/preprocessor/seq/for_each_i.hpp:27:55:
>>>> note: expanded from macro 'BOOST_PP_SEQ_FOR_EACH_I'
>>>> #    define BOOST_PP_SEQ_FOR_EACH_I(macro, data, seq)
>>>> BOOST_PP_FOR((macro, data, seq (nil), 0), BOOST_PP_SEQ_FOR_EACH_I_P,
>>>> BOOST_PP_SEQ_FOR_EACH_I_O, BOOST_PP_SEQ_FOR_EACH_I_M)
>>>>                                                        ^
>>>> /usr/local/boost_1_55_0/boost/preprocessor/repetition/for.hpp:27:23:
>>>> note: expanded from macro 'BOOST_PP_FOR'
>>>> # define BOOST_PP_FOR BOOST_PP_CAT(BOOST_PP_FOR_,
>>>> BOOST_PP_AUTO_REC(BOOST_PP_FOR_P, 256))
>>>>                        ^
>>>> /usr/local/boost_1_55_0/boost/preprocessor/cat.hpp:22:32: note: 
>>>> expanded
>>>> from macro 'BOOST_PP_CAT'
>>>> #    define BOOST_PP_CAT(a, b) BOOST_PP_CAT_I(a, b)
>>>>                                 ^
>>>> /usr/local/boost_1_55_0/boost/preprocessor/cat.hpp:29:34: note: 
>>>> expanded
>>>> from macro 'BOOST_PP_CAT_I'
>>>> #    define BOOST_PP_CAT_I(a, b) a ## b
>>>>                                   ^
>>>> <scratch space>:130:1: note: expanded from here
>>>> BOOST_PP_FOR_1
>>>> ^
>>>> /usr/local/boost_1_55_0/boost/preprocessor/repetition/detail/for.hpp:22:37: 
>>>>
>>>>
>>>> note: expanded from macro 'BOOST_PP_FOR_1'
>>>> # define BOOST_PP_FOR_1(s, p, o, m) 
>>>> BOOST_PP_FOR_1_C(BOOST_PP_BOOL(p(2,
>>>> s)), s, p, o, m)
>>>>                                      ^
>>>> /usr/local/boost_1_55_0/boost/preprocessor/repetition/detail/for.hpp:279:42: 
>>>>
>>>>
>>>> note: expanded from macro 'BOOST_PP_FOR_1_C'
>>>> # define BOOST_PP_FOR_1_C(c, s, p, o, m) BOOST_PP_IIF(c, m,
>>>> BOOST_PP_TUPLE_EAT_2)(2, s) BOOST_PP_IIF(c, BOOST_PP_FOR_2,
>>>> BOOST_PP_TUPLE_EAT_4)(BOOST_PP_EXPR_IIF(c, o)(2, s), p, o, m)
>>>>                                           ^
>>>> /usr/local/boost_1_55_0/boost/preprocessor/control/iif.hpp:18:37: 
>>>> note:
>>>> expanded from macro 'BOOST_PP_IIF'
>>>> #    define BOOST_PP_IIF(bit, t, f) BOOST_PP_IIF_I(bit, t, f)
>>>>                                      ^
>>>> /usr/local/boost_1_55_0/boost/preprocessor/control/iif.hpp:25:39: 
>>>> note:
>>>> expanded from macro 'BOOST_PP_IIF_I'
>>>> #    define BOOST_PP_IIF_I(bit, t, f) BOOST_PP_IIF_ ## bit(t, f)
>>>>                                        ^
>>>> <scratch space>:136:1: note: expanded from here
>>>> BOOST_PP_IIF_0
>>>> ^
>
>
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