title: check if class exists within file without requiring/including
body: <p>Is there a way to check if class exists within a file without including/requiring the class?</p>
  
  <p>Something like: <code>class_in_file($file);</code></p>
  
  <p>As I already mentioned, I know this can be done with requiring/including the class and then looking up <code>class_exists($class);</code>, but any other ways?</p>