return MetricValues{
		values:      make(map[MetricName][]metricValue, len(d)),
		descriptors: d,
	}
}

// ToPromMetrics - converts the internal metric values to Prometheus
// adding the given name prefix. The extraLabels are added to each metric as
// constant labels.
func (m *MetricValues) ToPromMetrics(namePrefix string, extraLabels map[string]string,
) []prometheus.Metric {
	metrics := make([]prometheus.Metric, 0, len(m.values))