title: How can I pass nested parameter value to service in Symfony2
body: <p>For example, in my <em>services.yml</em> file next code:</p>
  
  <pre><code>parameters:
      social:
          facebook:
              app_id: 123456789
              secret: dkl41a5dw1daw11d1wa135451awwlflaw
          google:
              id: 12548411654
  
  services:
      bw.user.social:
          class: BW\UserBundle\Service\SocialService
          arguments: [%social.facebook%]
  </code></pre>
  
  <p>This method does not work. I can use this:</p>
  
  <pre><code>services:
      bw.user.social:
          class: BW\UserBundle\Service\SocialService
          arguments: [%social%]
  </code></pre>
  
  <p>But it's not exactly what I need. How can I pass <strong>only</strong> facebook value without google and , it's very important, <strong>not change</strong> parameters structure?</p>