Function fold

metrics/tenant_registries.go:470–486

fold returns value computed from multiple metrics, using folding function. if there are no metrics, it returns NaN.

(mf *dto.MetricFamily, fn func(*dto.Metric) float64, foldFn func(val, res float64) float64)

// fold returns value computed from multiple metrics, using folding function. if there are no metrics, it returns NaN.
func fold(mf *dto.MetricFamily, fn func(*dto.Metric) float64, foldFn func(val, res float64) float64) float64 {
	result := math.NaN()

	for _, m := range mf.GetMetric() {
		value := fn(m)
		if math.IsNaN(value) {
			continue
		}
		if math.IsNaN(result) {
			result = value
		} else {
			result = foldFn(value, result)
		}
	}

	return result
}

// This works even if m is nil, m.Counter is nil or m.Counter.Value is nil (it returns 0 in those cases)
func counterValue(m *dto.Metric) float64 { return m.GetCounter().GetValue() }