Hi list, I'm a big fan of both foreach and auto facilities provided by Boost and was thinking of merging the two. I searched in the list archives and saw the question was discussed earlier but didn't find a clear reason on why it shouldn't be done. How bad is this quite simple solution :
#define AUTO_FOREACH(VAR, COL) \ BOOST_FOREACH_PREAMBLE() \ if (boost::foreach_detail_::auto_any_t BOOST_FOREACH_ID(_foreach_col) = BOOST_FOREACH_CONTAIN(COL)) {} else \ if (boost::foreach_detail_::auto_any_t BOOST_FOREACH_ID(_foreach_cur) = BOOST_FOREACH_BEGIN(COL)) {} else \ if (boost::foreach_detail_::auto_any_t BOOST_FOREACH_ID(_foreach_end) = BOOST_FOREACH_END(COL)) {} else \ for (bool BOOST_FOREACH_ID(_foreach_continue) = true; \ BOOST_FOREACH_ID(_foreach_continue) && !BOOST_FOREACH_DONE(COL); \ BOOST_FOREACH_ID(_foreach_continue) ? BOOST_FOREACH_NEXT(COL) : (void)0) \ if (boost::foreach_detail_::set_false(BOOST_FOREACH_ID(_foreach_continue))) {} else \ for (BOOST_AUTO(VAR, BOOST_FOREACH_DEREF(COL)); !BOOST_FOREACH_ID(_foreach_continue); BOOST_FOREACH_ID(_foreach_continue) = true)
#define auto_foreach AUTO_FOREACH
It is basically the same code as BOOST_FOREACH (from boost 1.39) except that last line where I added the BOOST_AUTO in the for initialization. auto_foreach can then be used as :
auto_foreach(i, container) // i is a copy auto_foreach(&i, container) // i is a reference auto_foreach(const &i, container) // is a const reference
This seems pretty cool and I don't see obvious pitfalls though I don't know the exact magic behind both auto & foreach. Am I living dangerously by using this auto_foreach ? Thanks, -- Maxime