Shared Container Iterator

The purpose of the shared container iterator is to attach the lifetime of a container to the lifetime of its iterators. In other words, the container will not be deleted until after all its iterators are destroyed. The shared container iterator is typically used to implement functions that return iterators over a range of objects that only need to exist for the lifetime of the iterators. By returning a pair of shared iterators from a function, the callee can return a heap-allocated range of objects whose lifetime is automatically managed.

The shared container iterator augments an iterator over a shared container. It maintains a reference count on the shared container. If only shared container iterators hold references to the container, the container's lifetime will end when the last shared container iterator over it is destroyed. In any case, the shared container is guaranteed to persist beyond the lifetime of all the iterators. In all other ways, the shared container iterator behaves the same as its base iterator.

Synopsis

namespace boost {
  template <typename Container>
  class shared_container_iterator;

  template <typename Container>
  shared_container_iterator<Container>
  make_shared_container_iterator(typename Container::iterator base, 
    boost::shared_ptr<Container> const& container);

  std::pair<
    typename shared_container_iterator<Container>,
    typename shared_container_iterator<Container>
  >
  make_shared_container_range(boost::shared_ptr<Container> const& container);
}

The Shared Container Iterator Type

template <typename Container> class shared_container_iterator;

Example

The following example illustrates how to create an iterator that regulates the lifetime of a reference counted std::vector. Though the original shared pointer ints ceases to exist after set_range() returns, the shared_counter_iterator objects maintain references to the underlying vector and thereby extend the container's lifetime.

shared_iterator_example1.cpp:

#include "shared_container_iterator.hpp"
#include "boost/shared_ptr.hpp"
#include <algorithm>
#include <iostream>
#include <vector>

typedef boost::shared_container_iterator< std::vector<int> > iterator;


void set_range(iterator& i, iterator& end)  {

  boost::shared_ptr< std::vector<int> > ints(new std::vector<int>());
  
  ints->push_back(0);
  ints->push_back(1);
  ints->push_back(2);
  ints->push_back(3);
  ints->push_back(4);
  ints->push_back(5);
  
  i = iterator(ints->begin(),ints);
  end = iterator(ints->end(),ints);
}


int main() {

  iterator i,end;

  set_range(i,end);

  std::copy(i,end,std::ostream_iterator<int>(std::cout,","));
  std::cout.put('\n');

  return 0;
}

0,1,2,3,4,5,

Template Parameters

Model of

Members

shared_container_iterator(Container::iterator const& it,
                          boost::shared_ptr<Container> const& container)

The Shared Container Iterator Object Generator

template <typename Container>
shared_container_iterator<Container>
make_shared_container_iterator(Container::iterator base,
                               boost::shared_ptr<Container> const& container)

Example

shared_iterator_example2.cpp:

#include "shared_container_iterator.hpp"
#include "boost/shared_ptr.hpp"
#include <algorithm>
#include <iterator>
#include <iostream>
#include <vector>


template <typename Iterator>
void print_range_nl (Iterator begin, Iterator end) {
  typedef typename std::iterator_traits<Iterator>::value_type val;
  std::copy(begin,end,std::ostream_iterator<val>(std::cout,","));
  std::cout.put('\n');
}


int main() {

  typedef boost::shared_ptr< std::vector<int> > ints_t;
  {
    ints_t ints(new std::vector<int>());

    ints->push_back(0);
    ints->push_back(1);
    ints->push_back(2);
    ints->push_back(3);
    ints->push_back(4);
    ints->push_back(5);

    print_range_nl(boost::make_shared_container_iterator(ints->begin(),ints),
		   boost::make_shared_container_iterator(ints->end(),ints));
  }
  


  return 0;
}

The Shared Container Iterator Range Generator

template <typename Container>
std::pair<
  shared_container_iterator<Container>,
  shared_container_iterator<Container>
>
make_shared_container_range(boost::shared_ptr<Container> const& container);

std::make_pair(make_shared_container_iterator(container->begin(),container),
               make_shared_container_iterator(container->end(),container));

Example

shared_iterator_example3.cpp:

#include "shared_container_iterator.hpp"
#include "boost/shared_ptr.hpp"
#include "boost/tuple/tuple.hpp" // for boost::tie
#include <algorithm>              // for std::copy
#include <iostream>              
#include <vector>


typedef boost::shared_container_iterator< std::vector<int> > iterator; 

std::pair<iterator,iterator>
return_range() {
  boost::shared_ptr< std::vector<int> > range(new std::vector<int>());
  range->push_back(0);
  range->push_back(1);
  range->push_back(2);
  range->push_back(3);
  range->push_back(4);
  range->push_back(5);
  return boost::make_shared_container_range(range);
}


int main() {


  iterator i,end;
  
  boost::tie(i,end) = return_range();

  std::copy(i,end,std::ostream_iterator<int>(std::cout,","));
  std::cout.put('\n');

  return 0;
}

© Copyright 2003 The Trustees of Indiana University. Use, modification and distribution is subject to the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)