title: Check if a function exists in specific file?
body: <p>I would like to check if the <code>$this-&gt;_controller</code> function <code>foo</code> exist before I call it.</p>
  
  <p><strong>Example of call:</strong></p>
  
  <pre><code>call_user_func_array([$this-&gt;_controller, $this-&gt;_url[1]]);
  </code></pre>
  
  <p>This will call the function <code>url[1]</code> in the controller inserted in the URL so, basically:</p>
  
  <pre><code>webserver/backend/foo
  </code></pre>
  
  <p>I want check if foo actually exists in the back-end.</p>
  
  <p>How can I do this?</p>