code: func NewAtomicWriteSet(tmpDir string) (*AtomicWriteSet, error) {
  	td, err := ioutil.TempDir(tmpDir, "write-set-")
  	if err != nil {
  		return nil, err
  	}
  
  	return &AtomicWriteSet{
  		root: td,
  	}, nil
  }
docs: // NewAtomicWriteSet creates a new atomic write set to
  // atomically create a set of files. The given directory
  // is used as the base directory for storing files before
  // commit. If no temporary directory is given the system
  // default is used.