private function readConfig()
 {
     if (!$this->filename) {
         throw new \RuntimeException('A valid configuration file must be passed before reading the config.');
     }
     if (!file_exists($this->filename)) {
         throw new \InvalidArgumentException(sprintf("The config file '%s' does not exist.", $this->filename));
     }
     if ($this->driver->supports($this->filename)) {
         return $this->driver->load($this->filename);
     }
     throw new \InvalidArgumentException(sprintf("The config file '%s' appears to have an invalid format.", $this->filename));
 }
 function supports($filename)
 {
     return $this->driver->supports($filename);
 }