code: func NewRegisteredFunctionalGauge(name string, r Registry, f func() int64) Gauge {
  	c := NewFunctionalGauge(f)
  	if nil == r {
  		r = DefaultRegistry
  	}
  	r.Register(name, c)
  	return c
  }
docs: // NewRegisteredFunctionalGauge constructs and registers a new StandardGauge.