title: static_cast with boost::shared_ptr?
body: <p>What is the equivalent of a <code>static_cast</code> with <code>boost::shared_ptr</code>?</p>
  
  <p>In other words, how do I have to rewrite the following </p>
  
  <pre><code>Base* b = new Derived();
  Derived* d = static_cast&lt;Derived*&gt;(b);
  </code></pre>
  
  <p>when using <code>shared_ptr</code>?</p>
  
  <pre><code>boost::shared_ptr&lt;Base&gt; b(new Derived());
  boost::shared_ptr&lt;Derived&gt; d = ???
  </code></pre>