title: How to concatenate a string, a parameter and a function return result in Symfony Expression Language
body: <p>I'm using Symfony 2.4 and it's Expression Language component. In one of my service definitions, I want to use an argument with <code>type="expression"</code>. How is it possible to concatenate the following four components using expression language:</p>
  
  <ol>
  <li><code>service('kernel').getCacheDir()</code>  A function result</li>
  <li><code>"/"</code> Just a slash</li>
  <li><code>%router.cache_class_prefix%</code> A parameter</li>
  <li><code>%corebundle.route_provider.cache.class%</code> A parameter</li>
  </ol>
  
  <p>I hope I was clear in what I want to achieve. Below you see a part of the <code>services.xml</code> file where I want to use it. But this throws an error: <code>SyntaxError: Unexpected token "string" of value "/" around position 33.</code></p>
  
  <pre><code>&lt;parameters&gt;
      &lt;parameter key="corebundle.route_provider.cache.class"&gt;ZikulaRoutes&lt;/parameter&gt;
  &lt;/parameters&gt;
  &lt;services&gt;
      &lt;service id="corebundle.route_provider" class="%corebundle.route_provider.class%"&gt;
          &lt;call method="setCachePath"&gt;
              &lt;argument type="expression"&gt;service('kernel').getCacheDir() "/" %router.cache_class_prefix% %corebundle.route_provider.cache.class%&lt;/argument&gt;
          &lt;/call&gt;
      &lt;/service&gt;
  </code></pre>