Hello, I would like to do the following with Boost.Range: #include <vector> #include <boost/range/adaptor/transformed.hpp> #include <boost/range/join.hpp> #include <boost/foreach.hpp> using boost::adaptors::transformed; using boost::join; struct A { int x; }; struct B { int x; }; struct C { int x; }; struct to_C { C operator()(A a) const { return C{a.x}; } C operator()(B b) const { return C{b.x}; } }; int main() { std::vector<A> a; std::vector<B> b; BOOST_FOREACH(const C& c, join(a, b) | transformed(to_C())) { // do something } return 0; } Basically, I am joining two ranges with different value types (A and B), then transforming the resulting range with a polymorphic functor (to_C) that converts either of A or B to a common third type, C. When I try to loop through this resulting range, however, I get the following compiler errors: In file included from ../../lib/boost/boost/range/join.hpp:15:0, from test.cpp:3: ../../lib/boost/boost/range/detail/join_iterator.hpp: In member function 'A & boost::range_detail::join_iterator_union< vector<A>::iterator, vector<B>::iterator, A & >::dereference(unsigned int) const': ../../lib/boost/boost/range/detail/join_iterator.hpp:216:42: instantiated from 'boost::range_detail::join_iterator< vector<A>::iterator, vector<B>::iterator, A, A & , boost::random_access_traversal_tag >::A & boost::range_detail::join_iterator< vector<A>::iterator, vector<B>::iterator, A, A & , boost::random_access_traversal_tag >::dereference() const' ../../lib/boost/boost/iterator/iterator_facade.hpp:517:32: instantiated from 'static boost::range_detail::join_iterator< vector<A>::iterator, vector<B>::iterator, A, A & , boost::random_access_traversal_tag >::A & boost::iterator_core_access::dereference( const boost::range_detail::join_iterator< vector<A>::iterator, vector<B>::iterator, A, A & , boost::random_access_traversal_tag > & )' ../../lib/boost/boost/iterator/iterator_facade.hpp:643:67: instantiated from 'boost::iterator_facade<I, V, TC, R, D>::A & boost::iterator_facade< I, V, TC, R, D >::operator *() const' ../../lib/boost/boost/iterator/transform_iterator.hpp:121:31: instantiated from 'boost::detail::transform_iterator_base< to_C , boost::range_detail::join_iterator< vector<A>::iterator, vector<B>::iterator, A, A & , boost::random_access_traversal_tag >, boost::use_default, boost::use_default >::type::C boost::transform_iterator< UnaryFunction , boost::range_detail::join_iterator< vector<A>::iterator, vector<B>::iterator, A, A & , boost::random_access_traversal_tag >, boost::use_default, boost::use_default >::dereference() const' ../../lib/boost/boost/iterator/iterator_facade.hpp:517:32: instantiated from 'static boost::transform_iterator< to_C , boost::range_detail::join_iterator< vector<A>::iterator, vector<B>::iterator, A, A & , boost::random_access_traversal_tag >, boost::use_default, boost::use_default >::C boost::iterator_core_access::dereference( const boost::transform_iterator< to_C , boost::range_detail::join_iterator< vector<A>::iterator, vector<B>::iterator, A, A & , boost::random_access_traversal_tag >, boost::use_default, boost::use_default > & )' ../../lib/boost/boost/iterator/iterator_facade.hpp:643:67: instantiated from 'boost::iterator_facade< I, V, TC, R, D >::C boost::iterator_facade<I, V, TC, R, D>::operator *() const' ../../lib/boost/boost/foreach.hpp:748:58: instantiated from 'boost ::foreach_detail_::foreach_reference< boost::range_detail::transformed_range< to_C, const boost::joined_range<vector<A>, vector<B> > >, mpl_::bool_<true> >::ame boost::foreach_detail_::foreach_reference<T, C>::type = C boost ::foreach_detail_::deref( boost::foreach_detail_::const boost::foreach_detail_::auto_any_base & , boost::foreach_detail_::type2type< boost::range_detail::transformed_range< to_C, const boost::joined_range<vector<A>, vector<B> > >, mpl_::bool_<true> > * )' test.cpp:23:5: instantiated from here ../../lib/boost/boost/range/detail/join_iterator.hpp:71:37: error: no match for ternary 'operator?:' in '(selected != 0u) ? this->boost::range_detail ::join_iterator_union<vector<A>::iterator, vector<B>::iterator, A &> ::m_it2.vector<A>::iterator::operator *() : this->boost::range_detail ::join_iterator_union<vector<A>::iterator, vector<B>::iterator, A &> ::m_it1.vector<A>::iterator::operator *()' Is there a way to do this? Thanks, Nate.