Question

can one inside a loop in template over a DataObject somehow tell wether you’re at $Pos 24 but counted from bottom – something like:

<% if Pos = "-24" %>do stuff<% end_if %>
or like
<% if TotalItems - 24 = Pos %>do stuff<% end_if %>
or like
<% if Last(24) %>do stuff<% end_if %>

Answer 1

In Silverstripe 3, to be able to do:

<% if FromBottom(24) %>
  Hello
<% end_if %>

you’ll have to add MyCustomIteratorFunctions.php to your /code folder with the following contents:

<?php
class MyCustomIteratorFunctions implements TemplateIteratorProvider
{

  protected $iteratorPos;
  protected $iteratorTotalItems;

  public static function get_template_iterator_variables()
  {
    return array('FromBottom');
  }

  public function iteratorProperties($pos, $totalItems)
  {
    $this->iteratorPos = $pos;
    $this->iteratorTotalItems = $totalItems;
  }

  function FromBottom($num)
  {
    return (($this->iteratorTotalItems - $this->iteratorPos) == $num);
  }
}

as seen here: https://groups.google.com/forum/#!msg/silverstripe-dev/DVBtzkblZqA/PWxanKGKDYIJ