Sorting deque of boost tuples
std::deque<boost::tuple<unsigned int, unsigned int> > messages;

sort(messages.begin(), messages.end(), msg_sort_criteria);

bool msg_sort_criteria(boost::tuple<unsigned int, unsigned int> lhs, boost::tuple<unsigned int, unsigned int> rhs)
{
  return boost::get<1>(lhs) < boost::get<1>(rhs);
}

class Messages::MessageImpl{
private:
  std::deque<boost::tuple<unsigned int, unsigned int> > messages;

  bool msg_sort_criteria(boost::tuple<unsigned int, unsigned int> lhs, boost::tuple<unsigned int, unsigned int> rhs)
  {
    return boost::get<1>(lhs) < boost::get<1>(rhs);
  }

  void fn()
  {
    sort(msg_queue_.begin(), msg_queue_.end(), msg_sort_criteria);
  }
}

class Messages::MessageImpl{
private:
  std::deque<boost::tuple<unsigned int, unsigned int> > messages;

  static bool msg_sort_criteria(boost::tuple<unsigned int, unsigned int> lhs,
                                boost::tuple<unsigned int, unsigned int> rhs)
  {
    return boost::get<1>(lhs) < boost::get<1>(rhs);
  }

  void fn()
  {
    sort(msg_queue_.begin(), msg_queue_.end(), &MessageImpl::msg_sort_criteria);
  }
};