#include <boost/tuple/tuple.hpp>
#include <boost/multi_index_container.hpp>
#include <boost/multi_index/sequenced_index.hpp>
#include <boost/multi_index/key_extractors.hpp>
#include <boost/multi_index/ordered_index.hpp>

#include <string>

namespace bm = ::boost::multi_index;


// http://lists.boost.org/boost-users/2005/12/16088.php
template<typename Tuple,int N>
struct tuple_member_extractor
{
        typedef typename
        boost::tuples::element<N,Tuple>::type result_type;

        const result_type& operator()(const Tuple& t) const
        {
                return boost::tuples::get<N>(t);
        }
}; 


template<typename T>
class mutable_tuple_element
{
public:
        mutable_tuple_element(const T& t):t(t){}
        operator T&()const{return t;}
private:
        mutable T t;
};

namespace boost{

namespace tuples{

template<typename T>
class access_traits<mutable_tuple_element<T> >
{
        typedef T&       non_const_type;
        typedef T&       const_type;
        typedef const T& parameter_type;
};

} // namespace tuples

} // namespace boost


typedef boost::tuple<std::string, mutable_tuple_element<std::string> > element;


typedef bm::multi_index_container<
        element,
        bm::indexed_by<bm::ordered_unique
        <tuple_member_extractor<element, 0> > 
> > multi_t;

int main()
{
        multi_t test;

        test.insert(boost::make_tuple("a", "aa"));

        const element & ref = *test.find("a");
        
        std::string & s = ref.get<1>();
}