title: What is the best way to differentiate between derived classes of a base class?
body: <p>I have base class <code>BaseClass</code> and derived classes <code>DerivedA</code>, <code>DerivedB</code>, and <code>DerivedC</code> that all inherit <code>BaseClass</code>.</p>
  
  <p>I have another class, <code>ExternalClass</code> with a method that accepts a parameter of type <code>BaseClass</code>, but is actually passed a derived class. What is the best way to differentiate between these classes in <code>ExternalClass</code> if I wanted to perform a different action based on which derived class it received?</p>
  
  <p>I was thinking of doing a <code>Select</code> but I'm not exactly sure how.</p>