code: func (r *Registry) Reservoir(name string, tags []string) *Reservoir {
  	factory := func() interface{} { return NewReservoir() }
  	return r.fetchReservoir(name, tags, factory)
  }
docs: // Reservoir fetches an instrument from the registry or creates a new one.
  //
  // If another instrument type is already registered with the same
  // name/tags, a blank one will be returned and an error
  // will be logged to the Errors() channel.