#include <boost/iterator/iterator_adaptor.hpp>

struct Node
{
    Node* next() { return this; }
    Node* prev() { return this; }
    Node const* next() const  { return this; }
    Node const* prev() const { return this; }
};

template <class V>
struct iter
  : boost::iterator_adaptor<iter<V>, V*, V, boost::bidirectional_traversal_tag>
{
    typedef 
      boost::iterator_adaptor<iter<V>, V*, V, boost::bidirectional_traversal_tag> 
    super;

    iter() {}

    explicit iter(V* n)
      : super(n)
    {}
    
    template <class V2>
    iter(iter<V2> const& x, typename boost::enable_if_convertible<V2*,V*>::type* = 0)
      : super(x.base())
    {}

    friend class boost::iterator_core_access;

 private:
    void increment()
    { base_reference() = base()->next(); }

    void decrement()
    { base_reference() = base()->prev(); }
};

int main()
{
    typedef iter<Node> iterator;
    typedef iter<Node const> const_iterator;

    Node n;
    
    iterator x(&n);
    const_iterator y(&n);
    y = x;
    ++x;
}