in src/main/java/org/apache/sling/commons/metrics/internal/MetricsServiceImpl.java [199:209]
private <T> Gauge<T> registerGauge(String name, Supplier<T> supplier) {
com.codahale.metrics.Gauge<T> codahaleGauge = supplier::get;
@SuppressWarnings("rawtypes")
MetricSupplier<com.codahale.metrics.Gauge> metricSupplier = () -> codahaleGauge;
@SuppressWarnings("unchecked")
com.codahale.metrics.Gauge<T> g = registry.gauge(name, metricSupplier);
GaugeImpl<T> gauge = new GaugeImpl<>(g);
metrics.put(name, gauge);
return gauge;
}