Unfortunately this function and module_invoke() do not allow passing variables by reference.

To work around this, you can do something like this:

foreach (module_implements('my_hook') as $module) {
$function = $module . '_my_hook';
$function($var1, $var2);

And, make sure to have the ampersand in the hook declaration:

function my_module_my_hook(&$var1, &$var2) {
$var1 = 'do';
$var2 = 'stuff';

If you want to pass things by reference, it's likely that you want to do

= drupal_alter('my_type', $data);


There is an exception to passing by reference. If the arguments for the hook are Objects, then they are passed by reference. This is default behaviour of php: .

An example of this in action is with the feeds hook hook_feeds_after_parse()!feeds!feeds.api.php/fu...

The hook is called using module_invoke_all, but you can, for example, remove all the


and the feeds import won't do anything.