docker/policyconfiguration/naming.go
func DockerReferenceIdentity(ref reference.Named) (string, error) {
	res := ref.Name()
	tagged, isTagged := ref.(reference.NamedTagged)
	digested, isDigested := ref.(reference.Canonical)
	switch {
	case isTagged && isDigested: // Note that this CAN actually happen.
		return "", errors.Errorf("Unexpected Docker reference %s with both a name and a digest", reference.FamiliarString(ref))
	case !isTagged && !isDigested: // This should not happen, the caller is expected to ensure !reference.IsNameOnly()
		return "", errors.Errorf("Internal inconsistency: Docker reference %s with neither a tag nor a digest", reference.FamiliarString(ref))
	case isTagged:
		res = res + ":" + tagged.Tag()
	case isDigested:
		res = res + "@" + digested.Digest().String()
	default: // Coverage: The above was supposed to be exhaustive.
		return "", errors.New("Internal inconsistency, unexpected default branch")
	}
	return res, nil
}
func DockerReferenceIdentity(ref reference.Named) (string, error) {
	res := ref.Name()
	tagged, isTagged := ref.(reference.NamedTagged)
	digested, isDigested := ref.(reference.Canonical)
	switch {
	case isTagged && isDigested: // Note that this CAN actually happen.
		return "", errors.Errorf("Unexpected Docker reference %s with both a name and a digest", reference.FamiliarString(ref))
	case !isTagged && !isDigested: // This should not happen, the caller is expected to ensure !reference.IsNameOnly()
		return "", errors.Errorf("Internal inconsistency: Docker reference %s with neither a tag nor a digest", reference.FamiliarString(ref))
	case isTagged:
		res = res + ":" + tagged.Tag()
	case isDigested:
		res = res + "@" + digested.Digest().String()
	default: // Coverage: The above was supposed to be exhaustive.
		return "", errors.New("Internal inconsistency, unexpected default branch")
	}
	return res, nil
}
// DockerReferenceIdentity returns a string representation of the reference, suitable for policy lookup,
// as a backend for ImageReference.PolicyConfigurationIdentity.
// The reference must satisfy !reference.IsNameOnly().