code: func (f *Factory) Counter(options metrics.Options) metrics.Counter {
  	counter := &counter{
  		counters: make([]metrics.Counter, len(f.factories)),
  	}
  	for i, factory := range f.factories {
  		counter.counters[i] = factory.Counter(options)
  	}
  	return counter
  }
docs: // Counter implements metrics.Factory interface