On Mon, 27 Jun 2011 23:25:15 +0200, Mathias Gaunard wrote:
Consider something like
BOOST_FOREACH(std::pair<A, B> a, mymap)
this fails because the preprocessor sees it as three arguments.
Assuming BOOST_FOREACH was using STRIP_PARENS on its arguments, you could do
Chaos has a macro that does this called CHAOS_PP_DECODE (and a corresponding CHAOS_PP_ENCODE which is provided for symmetry). However, assuming BOOST_FOREACH doesn't use it, you can still do it... // 1.cpp #include <boost/foreach.hpp> #include <chaos/preprocessor/facilities/type.h> #include <chaos/preprocessor/recursion/rail.h> CHAOS_PP_WALL( BOOST_FOREACH( CHAOS_PP_TYPE(std::pair<A, B> a), mymap ) ) { /* ... */ } g++ -E -P -std=gnu++0x -I $BOOST_ROOT -I $CHAOS_ROOT -D CHAOS_PP_VARIADICS 1.cpp ...or, cleaned up... // 2.cpp #include <boost/foreach.hpp> #include <chaos/preprocessor/facilities/encode.h> #include <chaos/preprocessor/facilities/type.h> #include <chaos/preprocessor/recursion/rail.h> #define FOREACH(d, c) \ CHAOS_PP_WALL(BOOST_FOREACH( \ CHAOS_PP_TYPE(CHAOS_PP_DECODE(d)), \ c \ )) \ /**/ FOREACH((std::pair<A, B> a), mymap) { /* ... */ } g++ -E -P -std=gnu++0x -I $BOOST_ROOT -I $CHAOS_ROOT -D CHAOS_PP_VARIADICS 2.cpp How's that for black magic? Chaos calls this sort of thing a "rail" (in the railgun sense) because it sends nearly arbitrary stuff through any amount of macro machinery and expands it (and any number of copies of it) after it comes out the other side regardless of where it appears in the output. Regards, Paul Mensonides