Re: [Boost-users] [preprocessor]

3 Oct 2007


      Michael Fawcett wrote:
...
On 10/2/07, Josh Brown  wrote:
...
The root of my problem seems to stem from the fact that BOOST_PP_IF
expands both the true and false expressions before it does the if test
and just outputs the already expanded expression.  Is this correct; and
if so, is there a way around it?
Make the IF lazy.
...
...
Or are there any obvious other
solutions to my problem that the boost experts can suggest :)
You'll want to look into BOOST_PP_TUPLE_EAT -
http://www.boost.org/libs/preprocessor/doc/ref/tuple_eat.html
Exactly.

     #define GET_OPTIONAL_ELEMENT(r, data, elem) \
         BOOST_PP_IF( \
             BOOST_PP_EQUAL(BOOST_PP_SEQ_SIZE(elem), 3), \
             BOOST_PP_SEQ_ELEM, BOOST_PP_TUPLE_EAT(2) \
         )(2,elem)


Regards,
Tobias

Re: [Boost-users] [preprocessor]

Tobias Schwinger