class Preferences {
    private $props = array();
    private static $instance;
    private function __construct() { }
    public static function getInstance() {
        if ( empty( self::$instance ) ) {
            self::$instance = new Preferences();
        }
        return self::$instance;
    }
    public function setProperty( $key, $val ) {
        $this->props[$key] = $val;
    }

    public function getProperty( $key ) {
        return $this->props[$key];
    }
}
$pref = Preferences::getInstance();
$pref->setProperty( "name", "matt" );
unset( $pref ); // remove the reference
$pref2 = Preferences::getInstance();
print $pref2->getProperty( "name" ) ."\n"; // demonstrate value is not lost  it will print matt