title: Cast 'this' to std::shared_ptr
body: <p>I have a method on a class to make a particular instance an "active" instance:</p>
  
  <pre><code>void makeActive() { activeInstance = this; }
  </code></pre>
  
  <p>However it doesn't work since <code>activeInstance</code> has type <code>std::shared_ptr&lt; ClassName &gt;</code>. How can I cast <code>this</code> to <code>std::shared_ptr&lt;ClassName&gt;</code>?</p>