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: reference.go
    path of file: ./repos/docker-ce/components/cli/vendor/github.com/docker/distribution/reference
    
    the code of the file until where you have to start completion: // Package reference provides a general type to represent any way of referencing images within the registry.
// Its main purpose is to abstract tags and digests (content-addressable hash).
//
// Grammar
//
// 	reference                 
    
func getBestReferenceType(ref reference) Reference {
	if ref.Name() == "" {
		// Allow digest only references
		if ref.digest != "" {
			return digestReference(ref.digest)
		}
		return nil
	}
	if ref.tag == "" {
		if ref.digest != "" {
			return canonicalReference{
				namedRepository: ref.namedRepository,
				digest:          ref.digest,
			}
		}
		return ref.namedRepository
	}
	if ref.digest == "" {
		return taggedReference{
			namedRepository: ref.namedRepository,
			tag:             ref.tag,
		}
	}

	return ref
}