title: References between two smart pointers
body: <p>Reading this stackoverflow <a href="https://stackoverflow.com/a/5026705/245265">answer</a> :</p>
  
  <blockquote>
    <p>QWeakPointer - Do you sense a reoccurring pattern? Just as
    std::weak_ptr and boost::weak_ptr this is used in conjunction with
    QSharedPointer when you need references between two smart pointers
    that would otherwise cause your objects to never be deleted.</p>
  </blockquote>
  
  <p>My question is - could anybody explain me such situation on a simple example, when two referencing smart pointers could cause non-deleted objects? </p>
  
  <p>Thank you in advance..</p>