code: func (a Afero) TempFile(dir, prefix string) (f File, err error) {
  	return TempFile(a.Fs, dir, prefix)
  }
docs: // TempFile creates a new temporary file in the directory dir
  // with a name beginning with prefix, opens the file for reading
  // and writing, and returns the resulting *File.
  // If dir is the empty string, TempFile uses the default directory
  // for temporary files (see os.TempDir).
  // Multiple programs calling TempFile simultaneously
  // will not choose the same file.  The caller can use f.Name()
  // to find the pathname of the file.  It is the caller's responsibility
  // to remove the file when no longer needed.