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: manifold.go
    path of file: ./repos/juju/worker/apiaddressupdater
    
    the code of the file until where you have to start completion: // Copyright 2015 Canonical Ltd.
// Licensed under the AGPLv3, see LICENCE file for details.

package api
    
func (config ManifoldConfig) newWorker(a agent.Agent, apiCaller base.APICaller) (worker.Worker, error) {
	tag := a.CurrentConfig().Tag()

	// TODO(fwereade): use appropriate facade!
	var facade APIAddresser
	switch apiTag := tag.(type) {
	case names.UnitTag:
		facade = uniter.NewState(apiCaller, apiTag)
	case names.ApplicationTag:
		facade = caasoperator.NewClient(apiCaller)
	case names.MachineTag:
		facade = machiner.NewState(apiCaller)
	default:
		return nil, errors.Errorf("expected a unit or machine tag; got %q", tag)
	}

	setter := agent.APIHostPortsSetter{Agent: a}
	w, err := NewAPIAddressUpdater(Config{
		Addresser: facade,
		Setter:    setter,
		Logger:    config.Logger,
	})
	if err != nil {
		return nil, errors.Trace(err)
	}
	return w, nil
}