code: func (r FutureEstimateFeeResult) Receive() (float64, error) {
  	res, err := receiveFuture(r)
  	if err != nil {
  		return -1, err
  	}
  
  	// Unmarshal result as a getinfo result object.
  	var fee float64
  	err = json.Unmarshal(res, &fee)
  	if err != nil {
  		return -1, err
  	}
  
  	return fee, nil
  }
docs: // Receive waits for the response promised by the future and returns the info
  // provided by the server.