       </td>
</tr>
</tbody>
</table></div>
</div>
<br class="table-break"><p>
      A little familiarity with the type traits classes allows us to construct a
      single mapping that allows us to determine the type of parameter from the type
      of the contained class. The type traits classes provide a transformation <a class="link" href="reference/add_reference.html" title="add_reference">add_reference</a>, which
      adds a reference to its type, unless it is already a reference.
    </p>
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