How do you get template preprocess functions to fire on hook theme suggestions? If you have a theme function like theme_field() for instance. I know you can do something like this:

function THEMENAME_preprocess_field(&amp;$varialbes) {
  dpm($variables);
}


and that will print out the all the variables (if you have Devel enabled). Then I see theme_hook_suggestions like this "field__field_date__featured_event". However, when I try to do this:

function THEMENAME_preprocess_field__field_date__featured_event(&amp;$varialbes) {
  dpm($variables);
}


The above does not work at all. Why is this? Is it possible to use a preprocess function on a theme suggestion? or are theme suggestions just for theme overrides and not for preprocessing?

thanks!
You need to do this before you can do that...

/*
 * Implements hook_preprocess_field().
 */
function YOURTHEME_preprocess_field(&amp;$vars) {
    if ($vars['SOME_FIELD']) {
        $function = 'YOURTHEME_preprocess_field__'.$vars['SOME_FIELD'];
        if (function_exists($function)) {
            $function($vars);
        }
    }
}