WordPress Object Cache wrapper I'm working on that has support for group purging.

wp-smart-cache.php

<?php

if ( !class_exists( 'WP_Smart_Cache_v1' ) ) :

Class WP_Smart_Cache_v1 {
	static $instances = array();
	public function __construct() {
		if ( function_exists( 'wp_cache_add_global_groups' ) )
			wp_cache_add_global_groups( array( 'wp_smart_cache_global' ) );
	}

	public function instantiate( $group ) {
		self::$instances[(string) $group] = new WP_Smart_Cache_Group_v1( (string) $group );
	}
}

class WP_Smart_Cache_Group_v1 {
	protected $version;
	protected $group;
	protected $global = false;
	public function __construct( $group ) {
		$this->set_group( $group );
	}

	protected function set_group( $group ) {
		$this->group = (string) $group;
	}

	protected function wp_cache_group() {
		if ( is_null( $this->version ) ) {
			$wp_cache_group = 'wp_smart_cache' . $this->global ? '_global' : '';
			$this->version = wp_cache_get( $this->group, $wp_cache_group );
			if ( !$this->version )
				$this->version = $this->purge();
		}
		return "{$this->group}__{$this->version}";
	}

	protected function generate_key( $length = 8 ) {
		$chars = 'abcdefghijklmnopqrstuvwxyz0123456789';
		$key = '';
		for ( $i = 0; $i < $length; $i++ ) {
			$key .= substr($chars, wp_rand(0, strlen($chars) - 1), 1);
		}
		return $key;
	}

	public function set_global() {
		if ( function_exists( 'wp_cache_add_global_groups' ) )
			wp_cache_add_global_groups( array( $this->group ) );
		$this->global = true;
		return $this;
	}

	public function add( $key, $data, $expire = '' ) {
		return wp_cache_add( $key, $data, $this->wp_cache_group(), $expire );
	}

	public function set( $key, $data, $expire = '' ) {
		return wp_cache_set( $key, $data, $this->wp_cache_group(), $expire );
	}

	public function get( $key ) {
		return wp_cache_get( $key, $this->wp_cache_group() );
	}

	public function delete( $key ) {
		return wp_cache_delete( $key, $this->wp_cache_group() );
	}

	public function purge() {
		$wp_cache_group = 'wp_smart_cache' . $this->global ? '_global' : '';
		$this->version = $this->generate_key();
		wp_cache_set( $this->group, $this->version, $wp_cache_group );
		return $this->version;
	}

}

function wp_smart_cache_instantiate() {
	new WP_Smart_Cache_v1;
}

// Because we need to wait for wp_rand() to be available
add_action( 'plugins_loaded', 'wp_smart_cache_instantiate', 0 );


function wp_smart_cache( $group = NULL ) {
	if ( !isset( WP_Smart_Cache_v1::$instances[(string) $group] ) )
		WP_Smart_Cache_v1::instantiate( $group );
	return WP_Smart_Cache_v1::$instances[(string) $group];
}

endif;