AppBuilder.Build from https://github.com/AgencyPMG/go-from-scratch

app_builder.go

//Build uses config and its factory functions to build a new App.
//If err is nil, the returned App is ready to Run.
func (ab *AppBuilder) Build(config *config.Config) (app *App, err error) {
	var sqlRepo *sqlrepo.Repo
	var dbCloser io.Closer

	defer func() {
		if err != nil && dbCloser != nil {
			dbCloser.Close()
		}
	}()

	sqlRepo, dbCloser, err = ab.SQLRepoFactory(config)
	if err != nil {
		return nil, err
	}

	repos := NewRepos(sqlRepo)

	bus := ab.CBusFactory(repos)

	api := ab.APIFactory(bus, repos)

	server := ab.ServerFactory(config)

	return &App{
		server:   server,
		handler:  api.Handler(),
		dbCloser: dbCloser,
	}, nil
}