Re: [Boost-users] [Preprocessor] Compile error after change from Boost 1.55 to 1.57

Subject: Re: [Boost-users] [Preprocessor] Compile error after change from Boost 1.55 to 1.57
From: Edward Diener (eldiener_at_[hidden])
Date: 2015-02-27 10:27:49

On 2/27/2015 9:56 AM, Edward Diener wrote:
> On 2/27/2015 5:04 AM, Franz Alt wrote:
>> Hi,
>>
>> I've written some preprocessor directives to generate functions for a
>> class. With Boost 1.55 everything works fine with gcc and clang. When I
>> try to change to Boost 1.57 I've got some strange compile errors.
>>
>> I'm happy if someone could help.
>
> In your FUNCTION_DECL macro you have this line:
>
> BOOST_PP_IF(BOOST_PP_LIST_IS_NIL(BOOST_PP_TUPLE_TO_LIST(BOOST_PP_TUPLE_ELEM(1,
> tup))), \
>
> but with your second function of '(b)' there is only one tuple element
> so attempting BOOST_PP_TUPLE_ELEM(1,tup) on it is undefined behavior.
> Instead test the size of the tuple with BOOST_PP_TUPLE_SIZE and if it is
> only 1 then you know you don't have a second tuple element and can
> convert it to '()'. In other words instead of:
>
> BOOST_PP_IF(BOOST_PP_LIST_IS_NIL(BOOST_PP_TUPLE_TO_LIST(BOOST_PP_TUPLE_ELEM(1,
> tup))), \
>     (), \
>
> have
>
> BOOST_PP_IIF(BOOST_PP_EQUAL(BOOST_PP_TUPLE_SIZE(tup),1)), \
>     (), \

This should be:

BOOST_PP_IIF(BOOST_PP_EQUAL(BOOST_PP_TUPLE_SIZE(tup),1), \
     (), \

Also your

            BOOST_PP_SEQ_TO_TUPLE( \
              BOOST_PP_SEQ_TRANSFORM( \
                ADD_CONST_REF, \
                _, \
 
BOOST_PP_TUPLE_TO_SEQ(BOOST_PP_LIST_TO_TUPLE(BOOST_PP_TUPLE_TO_LIST(BOOST_PP_TUPLE_ELEM(1, 
tup)))) \
              ) \
            ) \

has to be moved to another macro since it is evaluated even when your 
'tup' only has a single element.

Correct is:

      #define FUNCTION_DECL_EMPTY(tup) ()

      #define FUNCTION_DECL_NOT_EMPTY(tup) \
            BOOST_PP_SEQ_TO_TUPLE( \
              BOOST_PP_SEQ_TRANSFORM( \
                ADD_CONST_REF, \
                _, \
 
BOOST_PP_TUPLE_TO_SEQ(BOOST_PP_LIST_TO_TUPLE(BOOST_PP_TUPLE_TO_LIST(BOOST_PP_TUPLE_ELEM(1, 
tup)))) \
              ) \
            )

      #define FUNCTION_DECL(r, data, tup) \
        double BOOST_PP_TUPLE_ELEM(0, tup) \
          BOOST_PP_IIF(BOOST_PP_EQUAL(BOOST_PP_TUPLE_SIZE(tup),1), \
            FUNCTION_DECL_EMPTY, \
            FUNCTION_DECL_NOT_EMPTY \
          ) (tup) \
        const;

>
> You can't rely on undefined behavior and your version relies on
> BOOST_PP_TUPLE_ELEM on an element which does not exist return nothing
> and on BOOST_PP_TUPLE_TO_LIST when presented with nothing for a tuple
> expanding to an empty list.
>
> The fact that this once worked is just a coincidence of the
> implementation details, and these have changed from 1.55 to 1.57.
>
>>
>> Thanks
>>
>> Franz
>>
>>
>> gcc 4.9.1 failed with error:
>>
>>      test.cpp:33:1: error: macro "BOOST_PP_SEQ_ELEM_III" requires 2
>> arguments, but only 1 given
>>         )
>>       ^
>>      test.cpp:33:1: error: macro "BOOST_PP_VARIADIC_ELEM_2" requires 4
>> arguments, but only 2 given
>>      test.cpp:60:1: error: macro "BOOST_PP_SEQ_ELEM_III" requires 2
>> arguments, but only 1 given
>>       MY_FUNCTION_BEGIN((b))
>>       ^
>>      test.cpp:60:1: error: macro "BOOST_PP_VARIADIC_ELEM_2" requires 4
>> arguments, but only 2 give
>>
>>
>> clang 3.5.0 failed with error:
>>
>>      test.cpp:30:3: error: too few arguments provided to function-like
>> macro invocation
>>        MY_FUNCTIONS( \
>>        ^
>>      test.cpp:25:25: note: expanded from macro 'MY_FUNCTIONS'
>>        BOOST_PP_SEQ_FOR_EACH(FUNCTION_DECL, _, seq)
>>                              ^
>>      ..../boost.1_57_0/boost/preprocessor/seq/for_each.hpp:26:67: note:
>> expanded from macro 'BOOST_PP_SEQ_FOR_EACH'
>>      #    define BOOST_PP_SEQ_FOR_EACH(macro, data, seq)
>> BOOST_PP_FOR((macro, data, seq (nil)), BOOST_PP_SEQ_FOR_EACH_P,
>> BOOST_PP_SEQ_FOR_EACH_O, BOOST_PP_SEQ_FOR_EACH_M)
>>                                                                        ^
>>
>> ..../boost.1_57_0/boost/preprocessor/repetition/detail/for.hpp:22:78:
>> 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)
>>
>> ^
>>      note: (skipping 18 expansions in backtrace; use
>> -fmacro-backtrace-limit=0 to see all)
>>      packages/boost/boost_i4/boost/preprocessor/seq/elem.hpp:22:39:
>> note: expanded from macro 'BOOST_PP_SEQ_ELEM'
>>      #    define BOOST_PP_SEQ_ELEM(i, seq) BOOST_PP_SEQ_ELEM_I(i, seq)
>>                                            ^
>>      packages/boost/boost_i4/boost/preprocessor/seq/elem.hpp:41:45:
>> note: expanded from macro 'BOOST_PP_SEQ_ELEM_I'
>>      #        define BOOST_PP_SEQ_ELEM_I(i, seq)
>> BOOST_PP_SEQ_ELEM_II(BOOST_PP_SEQ_ELEM_ ## i seq)
>>                                                  ^
>>      packages/boost/boost_i4/boost/preprocessor/seq/elem.hpp:43:62:
>> note: expanded from macro 'BOOST_PP_SEQ_ELEM_II'
>>      #    define BOOST_PP_SEQ_ELEM_II(im) BOOST_PP_SEQ_ELEM_III(im)
>>                                                                   ^
>>      packages/boost/boost_i4/boost/preprocessor/seq/elem.hpp:44:13:
>> note: macro 'BOOST_PP_SEQ_ELEM_III' defined here
>>      #    define BOOST_PP_SEQ_ELEM_III(x, _) x
>>
>>
>> The program is:
>>
>>      #include <iostream>
>>
>>      #ifndef BOOST_PP_VARIADICS
>>        #define BOOST_PP_VARIADICS
>>      #endif
>>
>>      #include <boost/preprocessor.hpp>
>>
>>      #define ADD_CONST_REF(op, data, elem) elem const &
>>
>>      #define FUNCTION_DECL(r, data, tup) \
>>        double BOOST_PP_TUPLE_ELEM(0, tup) \
>>
>> BOOST_PP_IF(BOOST_PP_LIST_IS_NIL(BOOST_PP_TUPLE_TO_LIST(BOOST_PP_TUPLE_ELEM(1,
>>
>> tup))), \
>>            (), \
>>            BOOST_PP_SEQ_TO_TUPLE( \
>>              BOOST_PP_SEQ_TRANSFORM( \
>>                ADD_CONST_REF, \
>>                _, \
>>
>> BOOST_PP_TUPLE_TO_SEQ(BOOST_PP_LIST_TO_TUPLE(BOOST_PP_TUPLE_TO_LIST(BOOST_PP_TUPLE_ELEM(1,
>>
>> tup)))) \
>>              ) \
>>            ) \
>>          ) \
>>        const;
>>
>>      #define MY_FUNCTIONS(seq) \
>>        BOOST_PP_SEQ_FOR_EACH(FUNCTION_DECL, _, seq)
>>
>>      class Foo
>>      {
>>      public:
>>        MY_FUNCTIONS( \
>>          ((a, (int))) \
>>          ((b)       ) \
>>        )
>>      };
>>
>>      #define ADD_ARG(op, data, elem) elem const & BOOST_PP_CAT(a_, elem)
>>
>>      #define MY_FUNCTION_BEGIN(tup) \
>>        double Foo::BOOST_PP_TUPLE_ELEM(0, tup) \
>>
>> BOOST_PP_IF(BOOST_PP_LIST_IS_NIL(BOOST_PP_TUPLE_TO_LIST(BOOST_PP_TUPLE_ELEM(1,
>>
>> tup))), \
>>            (), \
>>            BOOST_PP_SEQ_TO_TUPLE( \
>>              BOOST_PP_SEQ_TRANSFORM( \
>>                ADD_ARG, \
>>                _, \
>>
>> BOOST_PP_TUPLE_TO_SEQ(BOOST_PP_LIST_TO_TUPLE(BOOST_PP_TUPLE_TO_LIST(BOOST_PP_TUPLE_ELEM(1,
>>
>> tup)))) \
>>              ) \
>>            ) \
>>          ) const \
>>        {
>>
>>      #define MY_FUNCTION_END() }
>>
>>      MY_FUNCTION_BEGIN((a, (int)))
>>      {
>>        std::cout << "Foo::a(" << a_int << ")\n";
>>      }
>>      MY_FUNCTION_END()
>>
>>      MY_FUNCTION_BEGIN((b))
>>      {
>>        std::cout << "Foo::b()\n";
>>      }
>>      MY_FUNCTION_END()
>>
>>      int main()
>>      {
>>        Foo f;
>>        f.a(42);
>>        f.b();
>>
>>        return 0;
>>      }
>>
>>
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