class someInterface{
  //it's inherent in our concept of what "someInterface"
  //means that they can be compared and sorted.
  //hence we provide for this:

  virtual int cmp(const someInterface& rhs) = 0;

  //these need not be virtual:

  bool operator==(const someInterface& rhs)const
  {
    return cmp(rhs) == 0;
  }
  bool operator<(const someInterface& rhs)const
  {
    return cmp(rhs) < 0;
  }

  //all "someInterface"s can "process" an array of chars;
  //This isn't far removed from the characters method
  //on a SAX ContentHandler.

  virtual void process(const char* start, const char* end) const = 0;

  //often the user of someInterface has a string (indeed
  //that would be safer. Also, we define process in terms
  //of a sequence (first, last] but many people think of
  //arrays as defined in terms of an initial pointer and a
  //size (especially those who moved from C to C++:

  void process(const char* start, size_t size) const{
    process(start, start + size);
  }

  void process(const std::string& str) const{
    process(str.data(), str.length());
  }

  /*other functions yadda yadda*/
};