Primitve cached version of wp_nav_menu

cached_nav_menu.php

/**
 * cached_nav_menu
 *
 * primitive cache of wp_nav_menu using
 * WP Transient APIs
 *
 * @author Marcin Zaremba
 * @param $args arguments passed originally to wp_nav_menu
 */
function cached_nav_menu($args) {
    global $wp_query;

    // calculating object id and items cached before
    $cached_items = unserialize(get_transient('cached_nav_menu'));
    $object_id = empty($wp_query->queried_object_id) ? 0 : (int) $wp_query->queried_object_id;

    // if its single or main give the same key
    if(is_single() || $object_id == 0) {
        $object_key = md5(serialize($args) . '- single');
    }
    else {
        $object_key = md5(serialize($args) . '-' . $object_id);
    }

    // if it's first time cached
    if(!$cached_items)
        $cached_items = array();

    $res = '';

    if(isset($cached_items[$object_key])) {
        $res = $cached_items[$object_key];
    }
    else {
        // saving to cache
        $args['echo'] = false;
        $res = wp_nav_menu($args);

        $cached_items[$object_key] = $res;
        delete_transient('cached_nav_menu');
        set_transient('cached_nav_menu', serialize($cached_items));
    }

    echo $res;
}

/**
 * Delete from cache when menu update met
 */
function cached_nav_menu_update() {
    delete_transient('cached_nav_menu');
}

add_action('wp_update_nav_menu', 'cached_nav_menu_update');