roller.h

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#ifndef ROLLER_CLASS
#define ROLLER_CLASS
 
/*****************************************************************************\
*                                                                             *
*  Name   : roller                                                            *
*  Author : Chris Koeritz                                                     *
*                                                                             *
*******************************************************************************
* Copyright (c) 1996-$now By Author.  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 2 of   *
* the License or (at your option) any later version.  This is online at:      *
*     http://www.fsf.org/copyleft/gpl.html                                    *
* Please send any updates to: fred@gruntose.com                               *
\*****************************************************************************/
 
#include <basis/definitions.h>
 
namespace structures {
 
 
template <class contents>
class roller
{
public:
  roller(contents start_of_range, contents end_of_range);
 
  ~roller();
 
  // these report the constructor parameters.
  contents minimum() { return _start_of_range; }
  contents maximum() { return _end_of_range; }
 
  contents next_id();
 
  contents current() const;
 
  void set_current(contents new_current);
 
private:
  contents _current_id;  
  contents _start_of_range;  
  contents _end_of_range;  
};
 
 
 
class int_roller : public roller<int>
{
public:
  int_roller(int start_of_range, int end_of_range)
          : roller<int>(start_of_range, end_of_range) {}
};
 
 
// implementations below...
 
template <class contents>
roller<contents>::roller(contents start, contents end)
: _current_id(start), _start_of_range(start), _end_of_range(end) {}
 
template <class contents>
void roller<contents>::set_current(contents new_current)
{
  _current_id = new_current;
  if (_current_id >= _end_of_range) _current_id = _start_of_range;
}
 
template <class contents> roller<contents>::~roller() {}
 
template <class contents> contents roller<contents>::current() const
{ return _current_id; }
 
template <class contents> contents roller<contents>::next_id()
{
  contents to_return = _current_id;
  if (to_return == _end_of_range) {
    // somehow the id to return is at the end of the range.  this probably
    // means the end of range condition wasn't detected last time due to an
    // error in the parameters or the operation of == or ++ in the templated
    // class.
    _current_id = _start_of_range;
    to_return = _current_id;
  }
  _current_id++;  // next id.
  if (_current_id == _end_of_range) _current_id = _start_of_range;
    // reset the current position when hits the end of the range.
  return to_return;
}
 
} //namespace.
 
#endif