/**
* Returns the singleton instance.
*
* @param string $class
* @return string
* @throws Exception
*/
protected static function get_instance($class = __CLASS__)
{
if (__CLASS__ === $class) {
throw new Exception(__METHOD__ . ' must be overridden');
}
if (null === self::$_instances) {
self::$_instances = array();
}
if (@isset(self::$_instances[$class])) {
return self::$_instances[$class];
}
self::$_instances[$class] = new $class();
$instance = self::$_instances[$class];
return $instance;
}
