title: Ruby on Rails : symbol as argument in form_for
body: <p>I understand what is passed to the <code>form_for</code> method when doing something like :</p>
  
  <pre><code>&lt;% form_for(@user) do |f| %&gt; ... &lt;% end %&gt;
  </code></pre>
  
  <p>if <code>@user</code> is set in the controller. This is pretty obvious.</p>
  
  <p>But what happens when we pass <code>:user</code>, as I have seen in many examples ?</p>
  
  <pre><code>&lt;% form_for(:user) do |f| %&gt; ... &lt;% end %&gt;
  </code></pre>
  
  <p>When should I use the symbol version ?</p>