MrClay\Cli\Arg::__call PHP Method

    public function __call($name, array $args = array())
    {
        if (array_key_exists($name, $this->spec)) {
            $this->spec[$name] = true;
            if ($name === 'assertFile' || $name === 'assertDir') {
                $this->spec['mustHaveValue'] = true;
            }
        } else {
            throw new BadMethodCallException('Method does not exist');
        }
        return $this;
    }