Fragment caching function

fragment-caching.php

<?php
/**
 * Fragment caching function
 * see: https://css-tricks.com/wordpress-fragment-caching-revisited/
 *
 * Usage:
 * <?php fragment_cache('frc_footer', DAY_IN_SECONDS, function() { ?>
 * code to cache (loops etc)
 * <?php }); // end fragment_cache ?>
 */

// Exit if accessed directly
if ( !defined('ABSPATH') ) exit;


// Random prefix that will define / invalidate transients
function frc_prefix() {
    return get_option('frc_random_prefix');
}
add_action('fragment_cache_prefix', 'frc_prefix');


// Clear cache when saving a post
function clear_cache() {
    $random = rand(0,999);
    update_option('frc_random_prefix',$random);
}
add_action('save_post','clear_cache');


// Fragment cache
function fragment_cache($key, $ttl, $function) {

  $key = apply_filters('fragment_cache_prefix','fragment_cache_').$key;
  $output = get_transient($key);
  if ( empty($output) ) {
    ob_start();
    call_user_func($function);
    $output = ob_get_clean();
    set_transient($key, $output, $ttl);
  }
  echo $output;
}