text: /////////////////////////////////////////////////////////////////////////////
  //
  // (C) Copyright Ion Gaztanaga  2007.
  //
  // Distributed under the Boost Software License, Version 1.0.
  //    (See accompanying file LICENSE_1_0.txt or copy at
  //          http://www.boost.org/LICENSE_1_0.txt)
  //
  // See http://www.boost.org/libs/intrusive for documentation.
  //
  /////////////////////////////////////////////////////////////////////////////
  
  #ifndef BOOST_INTRUSIVE_TREE_NODE_HPP
  #define BOOST_INTRUSIVE_TREE_NODE_HPP
  
  #include <boost/intrusive/detail/config_begin.hpp>
  #include <iterator>
  #include <boost/intrusive/detail/pointer_to_other.hpp>
  #include <boost/intrusive/detail/mpl.hpp>
  
  namespace boost {
  namespace intrusive {
  
  template<class VoidPointer>
  struct tree_node
  {
     typedef typename pointer_to_other
        <VoidPointer
        ,tree_node<VoidPointer> >::type   node_ptr;
  
     node_ptr parent_, left_, right_;
  };
  
  template<class VoidPointer>
  struct tree_node_traits
  {
     typedef tree_node<VoidPointer> node;
  
     typedef typename boost::pointer_to_other
        <VoidPointer, node>::type              node_ptr;
     typedef typename boost::pointer_to_other
        <VoidPointer, const node>::type        const_node_ptr;
  
     static node_ptr get_parent(const_node_ptr n)
     {  return n->parent_;  }
  
     static void set_parent(node_ptr n, node_ptr p)
     {  n->parent_ = p;  }
  
     static node_ptr get_left(const_node_ptr n)
     {  return n->left_;  }
  
     static void set_left(node_ptr n, node_ptr l)
     {  n->left_ = l;  }
  
     static node_ptr get_right(const_node_ptr n)
     {  return n->right_;  }
  
     static void set_right(node_ptr n, node_ptr r)
     {  n->right_ = r;  }
  };
  
  /////////////////////////////////////////////////////////////////////////////
  //                                                                         //
  //                   Implementation of the tree iterator                   //
  //                                                                         //
  /////////////////////////////////////////////////////////////////////////////
  
  // tree_iterator provides some basic functions for a 
  // node oriented bidirectional iterator:
  template<class Container, bool IsConst>
  class tree_iterator
     :  public std::iterator
           < std::bidirectional_iterator_tag
           , typename detail::add_const_if_c
              <typename Container::value_type, IsConst>::type
           >
  {
     protected:
     typedef typename Container::real_value_traits   real_value_traits;
     typedef typename Container::node_algorithms     node_algorithms;
     typedef typename real_value_traits::node_traits node_traits;
     typedef typename node_traits::node              node;
     typedef typename node_traits::node_ptr          node_ptr;
     typedef typename boost::pointer_to_other
        <node_ptr, void>::type                       void_pointer;
     static const bool store_container_ptr = 
        detail::store_cont_ptr_on_it<Container>::value;
  
     public:
     public:
     typedef typename detail::add_const_if_c
        <typename Container::value_type, IsConst>
        ::type                                       value_type;
     typedef value_type & reference;
     typedef value_type * pointer;
  
     tree_iterator()
        : members_ (0, 0)
     {}
  
     explicit tree_iterator(node_ptr node, const Container *cont_ptr)
        : members_ (node, cont_ptr)
     {}
  
     tree_iterator(tree_iterator<Container, false> const& other)
        :  members_(other.pointed_node(), other.get_container())
     {}
  
     const node_ptr &pointed_node() const
     { return members_.nodeptr_; }
  
     tree_iterator &operator=(const node_ptr &node)
     {  members_.nodeptr_ = node;  return static_cast<tree_iterator&>(*this);  }
  
     public:
     tree_iterator& operator++() 
     { 
        members_.nodeptr_ = node_algorithms::next_node(members_.nodeptr_); 
        return static_cast<tree_iterator&> (*this); 
     }
     
     tree_iterator operator++(int)
     {
        tree_iterator result (*this);
        members_.nodeptr_ = node_algorithms::next_node(members_.nodeptr_);
        return result;
     }
  
     tree_iterator& operator--() 
     { 
        members_.nodeptr_ = node_algorithms::prev_node(members_.nodeptr_); 
        return static_cast<tree_iterator&> (*this); 
     }
     
     tree_iterator operator--(int)
     {
        tree_iterator result (*this);
        members_.nodeptr_ = node_algorithms::prev_node(members_.nodeptr_);
        return result;
     }
  
     bool operator== (const tree_iterator& i) const
     { return members_.nodeptr_ == i.pointed_node(); }
  
     bool operator!= (const tree_iterator& i) const
     { return !operator== (i); }
  
     value_type& operator*() const
     {  return *operator->();   }
  
     pointer operator->() const
     { return detail::get_pointer(this->get_real_value_traits()->to_value_ptr(members_.nodeptr_)); }
  
     const Container *get_container() const
     {
        if(store_container_ptr)
           return static_cast<const Container*>(members_.get_ptr());
        else
           return 0;
     }
  
     const real_value_traits *get_real_value_traits() const
     {
        if(store_container_ptr)
           return &this->get_container()->get_real_value_traits();
        else
           return 0;
     }
  
     tree_iterator end_iterator_from_it() const
     {
        return tree_iterator(node_algorithms::get_header(this->pointed_node()), this->get_container());
     }
  
     tree_iterator<Container, false> unconst() const
     {  return tree_iterator<Container, false>(this->pointed_node(), this->get_container());   }
  
     private:
     struct members
        :  public detail::select_constptr
           <void_pointer, store_container_ptr>::type
     {
        typedef typename detail::select_constptr
           <void_pointer, store_container_ptr>::type Base;
  
        members(const node_ptr &n_ptr, const void *cont)
           :  Base(cont), nodeptr_(n_ptr)
        {}
  
        node_ptr nodeptr_;
     } members_;
  };
  
  } //namespace intrusive 
  } //namespace boost 
  
  #include <boost/intrusive/detail/config_end.hpp>
  
  #endif //BOOST_INTRUSIVE_TREE_NODE_HPP
  