log.Fatalf("Attempting to initialize metric %q after metrics have started", def.Name)
	}
	d.known[def.Name] = def
}

// toHistogramViews works around https://github.com/open-telemetry/opentelemetry-go/issues/4003; in the future we can define
// this when we create the histogram.
func (d *metrics) toHistogramViews() []metric.Option {
	d.mu.Lock()
	defer d.mu.Unlock()
	d.started = true
	opts := []metric.Option{}