title: Wordpress Plugin add_meta_box to functions.php instead of inside plugin class
body: <p>I'm using a Wordpress plugin that adds a metabox to the post page via</p>
  
  <pre><code>add_meta_box( 'WPInsights', 'Insights', array(&amp;$this,'draw_insights'), 'post', 'normal', 'high' );
  </code></pre>
  
  <p>I want to add a meta box the same way through my <code>functions.php</code> file, but it says the first argument is supposed to be a valid callback (I assume it is referring to the use of <code>&amp;$this</code> because <code>WPInsights</code> is a class and <code>draw_insights()</code> is a function inside that class.</p>
  
  <p>How can I write an <code>add_meta_box</code> function for my <code>functions.php</code> file that uses the <code>WPInsights</code> class?</p>