loader:        loader,
	}
	mg.validate()
	return mg
}

// NewBucketMetricsGroup creates a new MetricsGroup for metrics with a `bucket`
// dimension (label).
//
// The `loader` function loads metrics from the cache and the system for a given
// list of buckets.
func NewBucketMetricsGroup(path collectorPath, descriptors []MetricDescriptor,
	loader BucketMetricsLoaderFn,
) *MetricsGroup {