174 � Elements of Object-oriented Design
class Configuration_DB { // ... } class Configuration_XML { // ... } $config = Configuration::getStore(Configuration::STORE_XML);
By taking the Singleton pattern a little further, we can implement the Registry pattern. This allows us to use any object as a Singleton without it being written specifically that way. The Registry pattern can be useful, for example, if, for the bulk of your application, you use the same database connection, but need to connect to an alternate database to perform a small set of tasks every now and then. If your DB class is implemented as a Singleton, this is impossible (unless you implement two separate classes, that is)—but a Registry makes it very easy: class Registry { private static $_register; public static function add(&$item, $name = null) { if (is_object($item) && is_null($name)) { $name = get_class($item); } elseif (is_null($name)) { $msg = "You must provide a name for non-objects"; throw new Exception($msg); } $name = strtolower($name); self::$_register[$name] = $item; } public static function &get($name) { $name = strtolower($name);
Licensed to 39713 - Mihails Tumkins (mihailt@gmail.com)
The Registry Pattern