public function prependDir(DirectoryInterface $dir, $namespace = self::MAIN_NAMESPACE)
{
// invalidate the cache
$this->cache = $this->errorCache = [];
if (!$dir->exists()) {
throw new LoaderError(sprintf('The "%s" directory does not exist.', $dir->getFullPath()));
}
if (!$dir->isDir()) {
throw new LoaderError(sprintf('The path "%s" is not a directory.', $dir->getFullPath()));
}
if (!isset($this->paths[$namespace])) {
$this->paths[$namespace][] = $dir;
} else {
array_unshift($this->paths[$namespace], $dir);
}
}