title: How to use a class without including its file?
body: <p>I have seen in many frameworks that you can use methods of an extended class without including the file. E.g.</p>
  
  <pre><code>Class MyController extends Controller {
  </code></pre>
  
  <p>When I do the same without a framework and try to call the method, I'll get:</p>
  
  <blockquote>
    <p>Fatal error: Class 'Helper' not found in ...</p>
  </blockquote>
  
  <p>Why am I not able to use that class without including its file? And why does that work for frameworks?</p>
  
  <p>Can I get rid of the including part if I used namespaces?</p>