[Boost-users] [multi-index][foreach] Iterating over a sequence index (worked in 1.46, broke in 1.47)

Subject: [Boost-users] [multi-index][foreach] Iterating over a sequence index (worked in 1.46, broke in 1.47)
From: Maxime van Noppen (maxime_at_[hidden])
Date: 2011-07-29 03:14:22

Hi,

I use BOOST_FOREACH to iterate of a BMI with a sequence index. The code 
used to work with Boost 1.46 and before, but broke with Boost 1.47. Am I 
doing something wrong ?

------------------------
#include <iostream>

# include <boost/multi_index/hashed_index.hpp>
# include <boost/multi_index/member.hpp>
# include <boost/multi_index/sequenced_index.hpp>
# include <boost/multi_index_container.hpp>
# include <boost/foreach.hpp>

using namespace ::boost::multi_index;

typedef multi_index_container< int, indexed_by< sequenced<> > > bmi_t;
typedef bmi_t::nth_index<0>::type seq_idx;

const seq_idx& ret(const seq_idx& idx) { return idx; }

int main()
{

   bmi_t b;

   seq_idx& seq = b.get<0>();

   // Works
   BOOST_FOREACH (int i, seq)
     std::cout << i << std::endl;

   // Doesn't compile
   BOOST_FOREACH (int i, ret(seq))
     std::cout << i << std::endl;
}

------------------------

Note that the offending part is the 'ret(seq)', without it, the code 
compiles.

The error with g++ 4.6.1 is:

> In file included from bmi.cc:9:0:
> /home/yabo/dev/boost/usr/include/boost/multi_index/sequenced_index.hpp: In destructor ‘boost::foreach_detail_::simple_variant<T>::~simple_variant() [with T = boost::multi_index::detail::sequenced_index<boost::multi_index::detail::nth_layer<1, int, boost::multi_index::indexed_by<boost::multi_index::sequenced<> >, std::allocator<int> >, boost::mpl::vector0<mpl_::na> >]’:
> /home/yabo/dev/boost/usr/include/boost/foreach.hpp:256:8:   instantiated from here
> /home/yabo/dev/boost/usr/include/boost/multi_index/sequenced_index.hpp:561:3: error: ‘boost::multi_index::detail::sequenced_index<SuperMeta, TagList>::~sequenced_index() [with SuperMeta = boost::multi_index::detail::nth_layer<1, int, boost::multi_index::indexed_by<boost::multi_index::sequenced<> >, std::allocator<int> >, TagList = boost::mpl::vector0<mpl_::na>]’ is protected
> /home/yabo/dev/boost/usr/include/boost/foreach.hpp:586:13: error: within this context
> /home/yabo/dev/boost/usr/include/boost/multi_index/sequenced_index.hpp: In constructor ‘boost::foreach_detail_::simple_variant<T>::simple_variant(const T&) [with T = boost::multi_index::detail::sequenced_index<boost::multi_index::detail::nth_layer<1, int, boost::multi_index::indexed_by<boost::multi_index::sequenced<> >, std::allocator<int> >, boost::mpl::vector0<mpl_::na> >]’:
> /home/yabo/dev/boost/usr/include/boost/foreach.hpp:648:95:   instantiated from ‘boost::foreach_detail_::auto_any<boost::foreach_detail_::simple_variant<T> > boost::foreach_detail_::contain(const T&, bool*) [with T = boost::multi_index::detail::sequenced_index<boost::multi_index::detail::nth_layer<1, int, boost::multi_index::indexed_by<boost::multi_index::sequenced<> >, std::allocator<int> >, boost::mpl::vector0<mpl_::na> >]’
> bmi.cc:28:3:   instantiated from here
> /home/yabo/dev/boost/usr/include/boost/multi_index/sequenced_index.hpp:549:3: error: ‘boost::multi_index::detail::sequenced_index<SuperMeta, TagList>::sequenced_index(const boost::multi_index::detail::sequenced_index<SuperMeta, TagList>&) [with SuperMeta = boost::multi_index::detail::nth_layer<1, int, boost::multi_index::indexed_by<boost::multi_index::sequenced<> >, std::allocator<int> >, TagList = boost::mpl::vector0<mpl_::na>]’ is protected
> /home/yabo/dev/boost/usr/include/boost/foreach.hpp:571:9: error: within this context
> /home/yabo/dev/boost/usr/include/boost/multi_index/sequenced_index.hpp: In copy constructor ‘boost::foreach_detail_::simple_variant<T>::simple_variant(const boost::foreach_detail_::simple_variant<T>&) [with T = boost::multi_index::detail::sequenced_index<boost::multi_index::detail::nth_layer<1, int, boost::multi_index::indexed_by<boost::multi_index::sequenced<> >, std::allocator<int> >, boost::mpl::vector0<mpl_::na> >, boost::foreach_detail_::simple_variant<T> = boost::foreach_detail_::simple_variant<boost::multi_index::detail::sequenced_index<boost::multi_index::detail::nth_layer<1, int, boost::multi_index::indexed_by<boost::multi_index::sequenced<> >, std::allocator<int> >, boost::mpl::vector0<mpl_::na> > >]’:
> /home/yabo/dev/boost/usr/include/boost/foreach.hpp:256:8:   instantiated from ‘boost::foreach_detail_::auto_any<boost::foreach_detail_::simple_variant<T> > boost::foreach_detail_::contain(const T&, bool*) [with T = boost::multi_index::detail::sequenced_index<boost::multi_index::detail::nth_layer<1, int, boost::multi_index::indexed_by<boost::multi_index::sequenced<> >, std::allocator<int> >, boost::mpl::vector0<mpl_::na> >]’
> bmi.cc:28:3:   instantiated from here
> /home/yabo/dev/boost/usr/include/boost/multi_index/sequenced_index.hpp:549:3: error: ‘boost::multi_index::detail::sequenced_index<SuperMeta, TagList>::sequenced_index(const boost::multi_index::detail::sequenced_index<SuperMeta, TagList>&) [with SuperMeta = boost::multi_index::detail::nth_layer<1, int, boost::multi_index::indexed_by<boost::multi_index::sequenced<> >, std::allocator<int> >, TagList = boost::mpl::vector0<mpl_::na>]’ is protected
> /home/yabo/dev/boost/usr/include/boost/foreach.hpp:578:13: error: within this context

Note that with clang++ 2.9 the code doesn't compile at all either with 
Boost 1.46 or Boost 1.47.

Thanks!

-- 
Maxime