text: //sDNA software for spatial network analysis 
  //Copyright (C) 2011-2019 Cardiff University
  
  //This program is free software: you can redistribute it and/or modify
  //it under the terms of the GNU General Public License as published by
  //the Free Software Foundation, either version 3 of the License, or
  //(at your option) any later version.
  
  //This program is distributed in the hope that it will be useful,
  //but WITHOUT ANY WARRANTY; without even the implied warranty of
  //MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  //GNU General Public License for more details.
  
  //You should have received a copy of the GNU General Public License
  //along with this program.  If not, see <https://www.gnu.org/licenses/>.
  
  //unique ids for edges and links generated by the network object
  
  template<class T> class UniqueIdGenerator;
  
  template <class T> struct UniqueId 
  {
  	size_t id;
  	explicit UniqueId (size_t i) : id(i) {}
  	UniqueId() : id(-1) {}
  	inline bool operator==(const UniqueId<T> &other) const
  	{
  		return (this->id==other.id);
  	}
  	typedef T indexed_class_type;
  };
  
  template <class ID> class IndexedObject
  {
  public:
  	virtual inline ID get_id() const = 0;
  };
  