class dll_t; 
 
class dll_node_t 
{ 
  friend class dll_t; 
 
public: 
  explicit dll_node_t (); 
 
  void data (void *_p_data) {p_data_ = _p_data;} 
  void *data () {return p_data_;} 
 
private: 
  dll_node_t *prev_; 
  dll_node_t *next_; 
  void *p_data_; 
}; 
 
class channel_t 
{ 
public: 
  channel_t () : node () 
  { 
    node_.data (reinterpret_cast <void *> (this)); 
  } 
 
private: 
  dll_node_t node_; 
}; 

template <typename T_NODE> class dll_t; 
 
template <typename T_DATA> class dll_node_t 
{ 
  friend class dll_t <dll_node_t <T_DATA> >; 
   
public: 
  explicit dll_node_t (); 
 
  void data (T_DATA *_p_data) {p_data_ = _p_data;} 
  T_DATA *data () {return p_data_;} 
   
private: 
  dll_node_t *prev_; 
  dll_node_t *next_; 
  T_DATA *p_data_; 
}; 
 
class channel_t 
{ 
public: 
  channel_t (): node_ () 
  { 
    node_.data (this); 
  } 
   
private: 
  dll_node_t <channel_t> node_; 
};