title: Access parent within own `ggproto` object
body: <p>I want to access <code>compute_group()</code> of the parent method within my own <code>ggproto</code> object. Here are two different working approaches, but don't know if any is the &quot;correct&quot; way to go:</p>
  <ol>
  <li><code>self$super()$compute_group(...)</code></li>
  <li><code>ggproto_parent(&lt;parent&gt;, self)$compute_group(...)</code></li>
  </ol>
  <p>Any (strong) opinions?</p>