error_handling_1.go

func WriteFile(...) (err error) {
  ...
  defer func() {
    if cerr := f.Close(); cerr != nil && err == nil {
      err = cerr
    }
  }()

  _, err = f.Write(data)
  return err
}

error_handling_2.go

func safeClose(c io.Closer, err *error) {
  if cerr := f.Close(); cerr != nil && *err == nil {
    *err = cerr
  }
}

func WriteFile(...) (err error) {
  ...
  defer safeClose(f, &err)

  _, err = f.Write(data)
  return err
}