Drupal 7: custom data caching - static variables, cache_set()/cache_get()

gistfile1.php

<?php

/**
 * See:
 * https://www.lullabot.com/blog/article/beginners-guide-caching-data-drupal-7
 */

// example 1
function my_module_function() {
  $my_data = &drupal_static(__FUNCTION__);
  if (!isset($my_data)) {
    // Do your expensive calculations here, and populate $my_data
    // with the correct stuff..
  }
  return $my_data;
}

// example 2
function my_module_function() {
  $my_data = &drupal_static(__FUNCTION__);
  if (!isset($my_data)) {
    if ($cache = cache_get('my_module_data')) {
      $my_data = $cache->data;
    }
    else {
      // Do your expensive calculations here, and populate $my_data
      // with the correct stuff..
      cache_set('my_module_data', $my_data, 'cache');
    }
  }
  return $my_data;
}

// example 3 - my example, rare case
function my_module_function() {
  $my_data = &drupal_static(__FUNCTION__);
  $my_data_helper = &drupal_static(__FUNCTION__ .'_helper');
  if (!isset($my_data_1)) {
    // $my_data_helper may take part in building of $my_data
  }
  return $my_data;
}

?>