public function find($class)
    {
        //Resolve the real identifier in case an alias was passed
        while(array_key_exists($class, $this->_aliases)) {
            $class = $this->_aliases[$class];
        }

        //Find the identifier
        if($this->offsetExists($class)) {
            $result = $this->offsetGet($class);
        } else {
            $result = null;
        }

        return $result;
    }