title: Opencart: call method from another controller
body: <p>I need to call in <strong>checkout/confirm.tpl</strong> file a custom function that i've made in <strong>controller/product.php</strong></p>
  
  <p>what's the best way to make this?</p>
  
  <p>i've tried this, but doesn't work:</p>
  
  <pre><code>$productController = $this-&gt;load-&gt;model('product/product');
  $productController-&gt;customFunction();
  </code></pre>