utility/projection_iterator_example.cpp

// (C) Copyright Jeremy Siek 2000. Permission to copy, use, modify, sell and
// distribute this software is granted provided this copyright notice appears
// in all copies. This software is provided "as is" without express or implied
// warranty, and with no claim as to its suitability for any purpose.

#include <boost/config.hpp>
#include <list>
#include <iostream>
#include <iterator>
#include <algorithm>
#include <string>
#include <boost/iterator_adaptors.hpp>

struct personnel_record {
  personnel_record(std::string n, int id) : m_name(n), m_ID(id) { }
  std::string m_name;
  int m_ID;
};

struct select_name {
  typedef personnel_record argument_type;
  typedef std::string result_type;
  const std::string& operator()(const personnel_record& r) const {
    return r.m_name;
  }
  std::string& operator()(personnel_record& r) const {
    return r.m_name;
  }
};

struct select_ID {
  typedef personnel_record argument_type;
  typedef int result_type;
  const int& operator()(const personnel_record& r) const {
    return r.m_ID;
  }
  int& operator()(personnel_record& r) const {
    return r.m_ID;
  }
};

int main(int, char*[])
{
  std::list<personnel_record> personnel_list;

  personnel_list.push_back(personnel_record("Barney", 13423));
  personnel_list.push_back(personnel_record("Fred", 12343));
  personnel_list.push_back(personnel_record("Wilma", 62454));
  personnel_list.push_back(personnel_record("Betty", 20490));

  // Example of using projection_iterator_generator
  // to print out the names in the personnel list.

  boost::projection_iterator_generator<select_name,
    std::list<personnel_record>::iterator>::type
    personnel_first(personnel_list.begin()),
    personnel_last(personnel_list.end());

  std::copy(personnel_first, personnel_last,
            std::ostream_iterator<std::string>(std::cout, "\n"));
  std::cout << std::endl;
  
  // Example of using projection_iterator_pair_generator
  // to assign new ID numbers to the personnel.
  
  typedef boost::projection_iterator_pair_generator<select_ID,
    std::list<personnel_record>::iterator,
    std::list<personnel_record>::const_iterator> PairGen;

  PairGen::iterator ID_first(personnel_list.begin()),
    ID_last(personnel_list.end());

  int new_id = 0;
  while (ID_first != ID_last) {
    *ID_first = new_id++;
    ++ID_first;
  }

  PairGen::const_iterator const_ID_first(personnel_list.begin()),
    const_ID_last(personnel_list.end());

  std::copy(const_ID_first, const_ID_last,
            std::ostream_iterator<int>(std::cout, " "));
  std::cout << std::endl;
  std::cout << std::endl;
  
  // Example of using make_const_projection_iterator()
  // to print out the names in the personnel list again.
  
  std::copy
    (boost::make_const_projection_iterator<select_name>(personnel_list.begin()),
     boost::make_const_projection_iterator<select_name>(personnel_list.end()),
     std::ostream_iterator<std::string>(std::cout, "\n"));

  return 0;
}