ner classes  <reference.html#associative-containers>`_

  - `ptr_set <ptr_set.html>`_
  - `ptr_multiset <ptr_multiset.html>`_
  - `ptr_map <ptr_map.html>`_
  - `ptr_multimap <ptr_multimap.html>`_
- `Indirected functions <indirect_fun.html>`_
- `Class nullable <reference.html#class-nullable>`_
- `Exception classes <reference.html#exception-classes>`_ -->
</div>
<div class="section">
<h1><a id="motivation" name="motivation">Motivation</a></h1>
<p>Whenever a programmer wants to have a container of pointers to
