#include <iostream>
#include <string>
#include <boost/shared_ptr.hpp>
#include <boost/make_shared.hpp>
#include <boost/bimap.hpp>
#include <boost/iterator/transform_iterator.hpp>

struct A
{
    std::string data;
    A(const std::string& s) : data(s) {}
};

typedef boost::bimap<unsigned int, boost::shared_ptr<A> > container_type;
typedef container_type::left_map::const_iterator base_const_iterator;

template <typename T>
struct makeIterConst : std::unary_function<base_const_iterator::value_type const &,
                                           std::pair<unsigned int const, boost::shared_ptr<T const> const> >
{
     std::pair<unsigned int const, boost::shared_ptr<T const> const> operator()
             (base_const_iterator::value_type const & orig) const
     {
         std::pair<int const, boost::shared_ptr<T const> const> newPair(orig.first, boost::const_pointer_cast<T const>(orig.second));
         return newPair;
     }
};

typedef boost::transform_iterator<makeIterConst<A>,
                                 base_const_iterator> const_iterator;

int main()
{
    container_type m;
    boost::shared_ptr<A> p = boost::make_shared<A>("foo");
    m.insert( container_type::value_type(1, p));

    //  using regular iterator
    for( base_const_iterator left_iter  = m.left.begin();
                             left_iter != m.left.end();
                           ++left_iter )
    {
        std::cout << left_iter->first << " --> " << left_iter->second->data << '\n';
        left_iter->second->data =  "bar"; // compiles
    }

    // using constified iterator
    for( const_iterator left_iter  = boost::make_transform_iterator(m.left.begin(), makeIterConst<A>() );
                        left_iter != boost::make_transform_iterator(m.left.end(), makeIterConst<A>() );
                      ++left_iter )
    {
        std::cout << left_iter->first << " --> " << left_iter->second->data << '\n';
//   the following will give a compilation error, as expected
//      left_iter->second->data =  "changed_foo";
    }
}