public function addFunction(&$function)
    {
        if (isset($this->_functions[$function->name()])) {
            $phpdoctor =& $this->_root->phpdoctor();
            echo "\n";
            $phpdoctor->warning('Found function '.$function->name().' again, overwriting previous version');
        }
        $this->_functions[$function->name()] =& $function;
    }