WordPress Fragment Caching convenience wrapper

gistfile1.aw

<?php
/*
Usage:
	$frag = new CWS_Fragment_Cache( 'unique-key', 3600 ); // Second param is TTL
	if ( !$frag->output() ) { // NOTE, testing for a return of false
		functions_that_do_stuff_live();
		these_should_echo();
		// IMPORTANT
		$frag->store();
		// YOU CANNOT FORGET THIS. If you do, the site will break.
	}
*/

class CWS_Fragment_Cache {
	const GROUP = 'cws-fragments';
	var $key;
	var $ttl;

	public function __construct( $key, $ttl ) {
		$this->key = $key;
		$this->ttl = $ttl;
	}

	public function output() {
		$output = wp_cache_get( $this->key, self::GROUP );
		if ( !empty( $output ) ) {
			// It was in the cache
			echo $output;
			return true;
		} else {
			ob_start();
			return false;
		}
	}

	public function store() {
		$output = ob_get_flush(); // Flushes the buffers
		wp_cache_add( $this->key, $output, self::GROUP, $this->ttl );
	}
}

@markjaquith It seems there could be a simpler API to do the same thing by using a wrapper function for a closure:

<?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;
}

See fork: https://gist.github.com/westonruter/5475349

It seems there could be a simpler API to do the same thing by using a wrapper function for a closure

I considered that, but there are two problems:

1. It requires PHP 5.3 (though, this is becoming less and less of an issue).
2. It changes variable scope.

#2 is the big one. I wanted something that I could wrap around existing template code with zero changes to the code inside. If the code inside is using global variables, that will cease working when wrapped in a closure.

What are the pros & cons of using WP object cache vs transients? http://codex.wordpress.org/Transients_API

@astrotim transients will fall back to database caching on installs without a persistent object caching backend. You might want this (caching a feed) or you might not (caching 2000 query results).

@markjaquith Can we use this as a wrapper to an ajax callback?

For example, I have an ajax call that does expensive db queries and it returns the results as json for creating a graph via javascript.
I'm asking cause you state at the usage comment that the functions inside the wrapper should echo something.

Could this class be extended or modified to take into account also output that isn't echo'ed but returned?

Have you tested this on WP Multisite? Didn't see any references to multisite in the WP object cache API documentation.

@markjaquith should I wrap add_action() on my genesis theme with this? e.g.

$frag = new CWS_Fragment_Cache( 'custom-header', 3600 ); // Second param is TTL
    if ( !$frag->output() ) { // NOTE, testing for a return of false

        add_action( 'genesis_header', 'my_custom_header' );

        // IMPORTANT
        $frag->store();
        // YOU CANNOT FORGET THIS. If you do, the site will break.
    }

I used this today and updated it to use transients API. Works like a charm. Thanks.

How to clean individual fragments on, let's say, custom post type save/update?