Fragment caching utility class for WordPress. Based off; https://gist.github.com/markjaquith/2653957

fragment-cache.php

<?php
/*
 * Plugin Name: Fragment Cache
 * Description: Fragment cache provider plugin
 * Version:     1.2
 * Author:      Zachary Scott
 */

namespace zacscott;

/**
 * Simple fragment cache utility which uses WP transients. Site transients are
 * used to support multi site installations.
 *
 * Use like so:
 *
 * 	$cache = new FragmentCache( 'my-fragment', 3600 ); // cache for an hour
 *  if ( ! $cache->output() ) :
 *
 *  	echo some_heavy_lifting_here();
 *
 *  	$cache->store(); // NOTE this is important otherwise it will break your site
 * 	endif;
 *
 * Based off the fragment cache by Mark Jaquith;
 * https://gist.github.com/markjaquith/2653957
 *
 * @author Zachary Scott <[email protected]>
 */
class FragmentCache {

	private $key;
	private $ttl;

	/**
	 *
	 * @param $key Unique key for this fragment cache.
	 * @param $ttl Time the fragment is cached for in seconds. If set to 0, it
	 * will ever expire.
	 */
	public function __construct( $key, $ttl ) {
		assert( ! empty( $key ) );
		assert( is_numeric( $ttl ) );

		$this->key = (string) $key;
		$this->ttl = (int) $ttl;

	}

	/**
	 * Output the fragment from the cache if present.
	 *
	 * @return boolean Whether the fragment was in the cache.
	 */
	public function output() {

		$output = get_site_transient( $this->get_key() );
		if ( ! empty( $output ) ) { // It was in the cache

			echo "<!-- frag {$this->key} - cached -->\n";
			echo $output;
			echo "<!-- /frag {$this->key} -->\n";

			return true;

		} else {

			echo "<!-- frag {$this->key} - building -->\n";
			ob_start();
			return false;

		}

	}

	/** Stored the recorded fragment output and stores it in the cache. */
	public function store() {

		$output = ob_get_flush();
		set_site_transient( $this->get_key(), $output, $this->ttl );

		echo "<!-- /frag {$this->key} -->\n";

	}

	/** Deletes the fragment from the cache */
	public function delete() {
		delete_site_transient( $this->get_key() );
	}

	// Returns the transient key for the cache
	private function get_key() {
		return 'frag-' . md5( $this->key ); // NOTE must be < 40 chars
	}

}