private function readSourceFile()
    {
        if (null == $this->source) {
            $path = $this->getInputFile();
            if (null === $path) {
                throw new \RuntimeException("View input file not specified.");
            }
            try {
                $this->source = \file_get_contents($path);
            } catch (\Exception $e) {
                throw new \RuntimeException(sprintf('View "%s" file can not be read', $path));
            }
        }
        return $this->source;
    }