Separating your theme's preprocess functions

Preprocess functions are often a major part of any Drupal theme. It is a vital part of themes but more than often it leads to very big template.php files. Today I stumbled upon a simple but brilliant way to reduce its size by separating its logic into nicely shaped and separated files.

It was when working together with Pelle Wessman at Good Old that I noticed something in his template.php (slightly modified):

function mytheme_preprocess(&$vars, $hook) {
  $filename = sprintf(
    drupal_get_path('theme', 'mytheme'),
    str_replace('_', '-', $hook)

  if (is_file($filename)) {

Then there was an accompanying preprocesses directory with files like

$block = $vars['block'];

$vars['attributes'] = array();
$vars['attributes']['class'] = 'block';

if (isset($block->view)) {
  $vars['attributes']['class'] .= ' block-view-' . views_css_safe($block->view->name);

Because the code is executed from within the scope of the hook_preprocess() implementation it has access to all its variables.

Brilliant, is it not? Apparently the idea originally comes from the Studio base theme. I just love finding these small improvements!