code: func (d *Dispatcher) NewServiceClient(serviceName string, c *Client) *DispatcherClient {
  	if len(d.serviceMap) == 0 || d.serviceMap[serviceName] == nil {
  		logPanic("gorpc.Dispatcher: service [%s] must be registered with AddService() before calling NewServiceClient()", serviceName)
  	}
  
  	return &DispatcherClient{
  		c:           c,
  		serviceName: serviceName,
  	}
  }
docs: // NewServiceClient returns a client suitable for calling methods
  // of the service with name serviceName registered via AddService().
  //
  // It is safe creating multiple service clients over a single underlying client.