particularly disturbing fragment of my new poliqarp binding (in progress)

makedict.go

func MakeDict(prefix string, strings []string) (dict *Dict, err error) {
	image_file_size := 0
	dict, err = nil, nil
	for _, s := range strings {
		// accomodate the string itself, length counter and zero-byte marker
		// for the reason of backwards debility
		image_file_size += len(s) + 5
	}
	image_file, err := os.Create(prefix + `.image`)
	defer image_file.Close()
	if err != nil {
		return
	}
	err = image_file.Truncate(int64(image_file_size))
	if err != nil {
		return
	}
	offset_file, err := os.Create(prefix + `.offset`)
	defer offset_file.Close()
	if err != nil {
		return
	}
	err = offset_file.Truncate(int64(len(strings) * 4))
	if err != nil {
		return
	}
	var (
		image      []byte
		raw_offset []byte
		offset     []uint32
		image_tip  uint32 = 0
	)
	image, err = MapFileFW(image_file)
	if err != nil {
		return
	}
	raw_offset, err = MapFileFW(offset_file)
	if err != nil {
		return
	}
	offset, err = Reslice32(raw_offset)
	if err != nil {
		return
	}
	for i, s := range strings {
		err = Put32(image, uint64(image_tip), uint32(len(s)+1))
		if err != nil {
			Unmap(image)
			Unmap(raw_offset)
			return nil, err
		}
		image_tip += 4
		offset[i] = image_tip
		copy(image[image_tip:], s)
		image_tip += uint32(len(s) + 1)
		image[image_tip-1] = 0
	}
	SyncMap(image)
	SyncMap(raw_offset)
	return &Dict{Image: image, Offset: offset}, err //should be nil?
}

Sorry, I forgot to mention that my message was kind of offtopic, unrelated to your original question on mailing list about error handling. Just a nit about the order of error checking vs defer x.Close().

Note that zero fd and nil *os.File are two different things, but yes, as I said, os.File's Close() handles both conditions: http://golang.org/src/pkg/os/file_unix.go#L92

However, when dealing, for example, with zip package, it's not the case, and this code:

zipFile, err := zip.OpenReader("filename.zip")
defer zipFile.Close()
if err != nil {
      return err
}

will throw runtime error if there's an error opening zip file, because zipFile.Close() is deferred before error checking and zipFile is nil, so the correct code is:

zipFile, err := zip.OpenReader("filename.zip")
if err != nil {
      return err
}
defer zipFile.Close()

The question is may there be an error in os.Open or os.Create which would leave us with an open fd?