code: func (m *metricMap) Collect(ch chan<- Metric) {
  	m.mtx.RLock()
  	defer m.mtx.RUnlock()
  
  	for _, metrics := range m.metrics {
  		for _, metric := range metrics {
  			ch <- metric.metric
  		}
  	}
  }
docs: // Collect implements Collector.