code: func (r *Registry) fetchCounter(name string, tags []string, factory func() interface{}) *Counter {
  	v := r.Fetch(name, tags, factory)
  	if i, ok := v.(*Counter); ok {
  		return i
  	}
  	r.handleFetchError("counter", name, tags, v)
  	return factory().(*Counter)
  }
docs: // --------------------------------------------------------------------