What causes the error "Call-time pass-by-reference has been deprecated?" My understanding is that objects in PHP 5.3 are all passed by reference so using the &amp;$ notation is not necessary. My problem is using date_views module where I'm getting this error.

Deprecated function: Call-time pass-by-reference has been deprecated in
 _registry_check_code() (line 2701 of C:\wamp\www\cruzr\includes\bootstrap.inc).


The affected lines of the code are:

  // $type is either 'interface' or 'class', so we only need the first letter to
  // keep the cache key unique.
  $cache_key = $type[0] . $name;
  if (isset($lookup_cache[$cache_key])) {
    exit;
    if ($lookup_cache[$cache_key]) {
      require_once DRUPAL_ROOT . '/' . $lookup_cache[$cache_key];
    }
    return (bool) $lookup_cache[$cache_key];
  }


How do I test if a variable is passed by reference? With several classes being loaded how do I approach debugging this problem?
The cause of the "Call-time pass-by-reference has been deprecated in
 _registry_check_code()" is a file that holds a class being loaded that contains a variable that is passed by reference that is not in a function definition. 

Drupal 7 requires PHP 5.2 or higher and PHP 5 always passes objects into functions by reference

This was a difficult bug to find because enabling a feature of the Date Views module is what triggered it. However, the problem was in the Workbench Moderation module. What I did was set the breakpoint in the debugger on function drupal_set_message() then worked back through the call stack till I found the offending variable.

Problem was not exactly in the Date module but was nonetheless triggered by the Date module in line 53 of date_views_fields.inc.

// If we don't have a filter handler, we don't need to do anything more.
if (!$handler = views_get_handler($table_name, $field_name, 'filter')) {
  continue; 
}


This would iterate through all the view's handlers including workbench_moderatioin_handler_filter_user_can_moderate which passed a variable by reference not in a function definition,     parent::options_form(&amp;$form, &amp;$form_state);. Simply the Workbench moderation module needs to be patched to reflect changes in code in PHP 5.3