Registry class -- will this work?

[Troutnut]

I'm pretty new to the whole idea of designing with patterns, so please correct me if I start to sound clueless here. But it seems that my application calls for a singleton registry, because I'll be using a single global instance of a few different objects, and thanks to help here I think I've got a way to do it. I'm just wondering if anyone sees obvious reasons why this won't work, or if it throws up any red flags or anything...

Here's Registry.php:

<?
class Registry {

	var $cache;

	function Registry() {
		$this->cache = array();
		}

	function setEntry($key, &$item) {
		$this->cache[$key] = &$item;
		}

	function isEntry($key) {
		return ($this->getEntry($key) !== null);

	function &get($key) {
		static $registry;
		if ($registry && $key) {
			return $registry->cache[$key];
			} else {
			$registry = new Registry();
			return $registry;
			}
		}
	}

$r = Registry::get();
$r->setEntry('database', new DatabaseObject());
$r->setEntry('session', new SessionObject()); 

?>

Then, in my other classes, I'd call it something like this:

function doSomething(){

	$database = Registry::get('database');
	$session = Registry::get('session');

	// Do stuff with them.

	}

[sweatje]

It looks like your "get()" method is a mixture between a getKey() and a getInstance() that I would avoid.

Also, with PHP4 you always want to catch the objects by reference:

$database =& Registry::get('database');
    $session =& Registry::get('session'); 

Also, with error_reporting(E_ALL) I suspect you will get some errors if you try to reference a key you have not yet set, I would code some array_key_exists($key, $this->cache)s in these in a few spots.

And, lastly, PHP4 does not store references in static variables. See my post #4 in this thread for more details.

HTH

[Shrike]

A did a similar thing with PHP 5 (didn't actually know there was a design pattern for this). Anyway, in PHP 5 you can take advantage of static member variables which makes the whole thing alot easier. Things are a bit more tricky with PHP 4. Hope it helps a bit.

abstract class Repository
{
    
    static private $repository = array();
    
    /**
    *    Returns a static instance of $class
    *    @param string $class
    *    @return obj $$class
    */
    final static function getInstance($class, $arg = NULL)
    {
        static $repository;
        
        if(is_array($arg))
        {
            $arg = implode(",", $arg);
        }
        if(!isset(Repository::$repository[$class]))
        {
            Repository::$repository[$class] = new $class($arg);
        }
        return Repository::$repository[$class];
    }
}
// Requests the current Singleton, or creates a new one.
Repository::getInstance("SqlQueryHandler"); 

[kyberfabrikken]

You may want to search theese forums for Singleton

[Travis S]

I would suggest taking a look at phpPatterns Registry article. That should give you a pretty good insight as to what to do. It also has a fully ready to use PHP4 Registry class as part of the examples.