RE: [boost] Preprocessor warning from BOOST_PP_SEQ_ELEM

From: Paul Mensonides (pmenso57_at_[hidden])
Date: 2005-03-02 06:21:33

> -----Original Message-----
> From: boost-bounces_at_[hidden] 
> [mailto:boost-bounces_at_[hidden]] On Behalf Of Edward Bishop

> My question is, how can I eliminate the warning. Thanks in 
> advance for any comments/advice.
> 
> 
> #  include <boost/preprocessor/library.hpp>
> 
> #define IS_SIMPLE(t)   BOOST_PP_NOT_EQUAL(3, BOOST_PP_SEQ_SIZE(t))
> #define PROPERTIES(t)  BOOST_PP_SEQ_ELEM(2,t)
> #define HAS_COLOR(t)   BOOST_PP_EQUAL(2, BOOST_PP_SEQ_ELEM(0, \
>                                                 PROPERTIES(t)))
> #define COLOR(t)       BOOST_PP_SEQ_ELEM(1, PROPERTIES(t))
> 
> 
> #define FSIMPLE(a, s, i, t)                                      \
>      BOOST_PP_SEQ_ELEM(0,t) is simple;
> 
> #define FCOMPLEX(a, s, i, t)                                      \
>      BOOST_PP_SEQ_ELEM(0,t) is complex \
>      BOOST_PP_IF(HAS_COLOR(t), and color is COLOR(t) , );
                                                       ^^^
This is undefined behavior in C++.  Should be:

#define FCOMPLEX(a, s, i, t) \
    BOOST_PP_SEQ_ELEM(0,t) is complex \
    BOOST_PP_EXPR_IF(HAS_COLOR(t), and color is COLOR(t)); \

> #define FCHOICE(a, s, i, t) \
>      BOOST_PP_IF(IS_SIMPLE(t), \
>          FSIMPLE(a, s, i, t), \
>          FCOMPLEX(a, s, i, t))

The IF here is not lazy.  Both the true and false cases are being evaluated, but
then one is discarded.  Should be:

#define FCHOICE(a, s, i, t) \
    BOOST_PP_IF(IS_SIMPLE(t), FSIMPLE, FCOMPLEX)(a, s, i, t)

Regards,
Paul Mensonides