title: Define operator! for shared_ptr<A>
body: <p>I have a problem with defining <code>operator !</code> for my class. I use <code>shared_ptr&lt;A&gt;</code> objects and I would like to use <code>!</code> on them.</p>
  <pre><code>shared_ptr&lt;a&gt; b;
  bool result = !b; // using my operator, not !shared_ptr
  </code></pre>
  <p>I tried few times but I'm getting ambiguous error.</p>