title: Import subclasses of a protocol
body: <p>The following class structure is given:</p>
  
  <pre><code>clprotocol.h
  cla
  cla1
  cla2
  cla3
  clb
  clb1
  clb2
  clb3
  
  foo.h
  </code></pre>
  
  <p>All classes implement the clprotocol. clxn are subclasses ob clx.</p>
  
  <p>I would like to inform foo.h of the existence of all classes which implement clprotocol.h. The straight forward way would be of course to import all headers in foo.h. But especially with large class clusters this is a very tedious task. Is there a more elegant way, also regarding the fact that if have to import this cluster in other classes, too?</p>
  
  <p>I feel like I am missing some basic principle here, but I can't put my finger on it...</p>