title: Convert a base class to a derived class
body: <p>I am wondering why this populates the derived class appropriately:</p>
  
  <pre><code>BaseClass bc = MethodThatReturnsBaseClassObject();
  DerivedClass dc = bc as DerivedClass;
  </code></pre>
  
  <p>But this creates a null derived class object:</p>
  
  <pre><code>DerivedClass dc = MethodThatReturnsBaseClassObject() as DerivedClass;
  </code></pre>