code: func NewGaugeFunc(opts prometheus.GaugeOpts, function func() float64) prometheus.GaugeFunc {
  	g := prometheus.NewGaugeFunc(opts, function)
  	prometheus.MustRegister(g)
  	return g
  }
docs: // NewGaugeFunc works like the function of the same name in the prometheus
  // package but it automatically registers the GaugeFunc with the
  // prometheus.DefaultRegisterer. If the registration fails, NewGaugeFunc panics.