public function initConstantPath($cst, $path_ref, $must_exists = false, $must_be_writable = false)
    {
        if (defined($cst)) {
            $this->addPath($path_ref, constant($cst), $must_exists, $must_be_writable);
        } else {
            throw new ErrorException(
                sprintf('Missing constant path "%s"!', $cst)
            );
        }
        return $this;
    }