title: Scope for private posts
body: <p>So I got a simple scope: </p>
  
  <pre><code>scope :visible_to, -&gt; (user) {user &amp;&amp; (user.premium? || user.admin?) ? all : where(:private =&gt; false || nil) }
  </code></pre>
  
  <p>The idea is that it shows (on index) a list of private and public post if the users role equals to <code>Premium</code> or <code>Admin</code>. Seems to work correctly when I am logged in as Admin or Premium. But if I'm not logged in or logged in as a <code>Standard</code> user ( default role) only nil post are displayed. How can I make it work for both standard and guest users? </p>