This operator enables the purchase history of a logged in user to be accessed in a product.tpl template to show different information to the user based on their order history.
This is primarily used to enabled downloadable purchases by using a template switch to show download links in place of the "add to cart" button for users who have already purchased the product.
Usage example:
Define the current users purchase list as an array in the full/product.tpl:

{def $my_buys = fetch(user, current_user)|my_purchases}
 

Put in download links if the current user has purchased the product:

 {if and($my_buys|array_keys|contains($node.object.id), array('Pending', 'Delivered')|contains($my_buys[$node.object.id]) )}
 
  <div class='attribute-download-purchased'>
         <p class='purchasestatus'>You have purchased this product</p>
         <p>Please use the link(s) below to download your files.</p>
 
          <div class="attribute-file">
            <p>
             {attribute_view_gui attribute=$node.object.data_map.file1}
            </p>
          </div>
  </div>