WordPress Fragment Caching convenience wrapper

gistfile1.php

<?php
/*
Usage:
	cache_fragment_output( 'unique-key', 3600, function () {
		functions_that_do_stuff_live();
		these_should_echo();
	});
*/

function cache_fragment_output( $key, $ttl, $function ) {
	$group = 'fragment-cache';
	$output = wp_cache_get( $key, $group );
	if ( empty($output) ) {
		ob_start();
		call_user_func( $function );
		$output = ob_get_clean();
		wp_cache_add( $key, $output, $group, $ttl );
	}
	echo $output;
}

Context:
http://markjaquith.wordpress.com/2013/04/26/fragment-caching-in-wordpress/
https://twitter.com/markjaquith/status/327768538179850241
https://twitter.com/westonruter/status/328316084941901824

Two reasons I didn't do it this way (I feel like I've said this before, but maybe it was to someone else):

1. Requires PHP 5.3 — I wanted "runs on any WordPress install" code.
2. Would likely require re-working the output code, if there is any reliance on global variables. I wanted something I could wrap around some random theme code and know that it would work every time.

But I agree that this is cleaner.