title: How to access current placeholder value?
body: <p>Symfony 3.4.
  I have annotations for my controller:</p>
  
  <pre><code>/**
   *
   * @Route("/{prefix}", requirements={"prefix":"daily_task|event"})
   */
  class TaskController extends Controller
  </code></pre>
  
  <p>and want to access current {prefix} value directly from controller's methods (which aren't routed actions). How to get it's value?</p>