You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: naming.go
    path of file: ./repos/octant/vendor/github.com/containers/image/v5/docker/policyconfiguration
    
    the code of the file until where you have to start completion: package policyconfiguration

import (
	"strings"

	"github.com/containers/image/v5/docker/reference"
	"github.com/pkg/errors"
)

// DockerReferenceIdentity returns a string representation of the reference, suitable for policy lookup,
// as a backend for ImageReferen
    
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
}