Pass arguments to subscriber callback

[joao-aguizo]

Hello, I wonder if it it is possible to pass an extra parameter to the subscriber callback. Does goroslib allow this somehow? What is the appropriate way of doing this? I checked the SubscriberConf struct definition,

https://github.com/aler9/goroslib/blob/978eeb6e825ee627aa2b33a765024ae9991139b2/subscriber.go#L24

and it does not seem have any field dedicated to this possibility. Is it possible to achieve this through the interface destined for the callback? The NewSubscriber function seems to limit this a bit

https://github.com/aler9/goroslib/blob/978eeb6e825ee627aa2b33a765024ae9991139b2/subscriber.go#L78

Context: my use case requires multiple topic subscriptions of the same type. For that I need to know to which topic, each message received belongs to. With rospy I would simply do something similar to what is suggested in the answer of this post https://answers.ros.org/question/231492/passing-arguments-to-callback-in-python/.

Apologies in advance if this is a golang specific question.

Best regards,
João Aguizo

[aler9]

Hello, one of the advantages of Golang with respect to Python is that it supports anonymous functions, therefore, you can add as many arguments as you want to the callback function, in this way

package main

import (
	"fmt"

	"github.com/aler9/goroslib"
	"github.com/aler9/goroslib/pkg/msgs/sensor_msgs"
)

func onMessage(msg *sensor_msgs.Imu, topicName string) {
	fmt.Printf("Incoming: %+v\n", msg)
        fmt.Println("topic name:", topicName)
}

func main() {
	// create a node and connect to the master
	n, err := goroslib.NewNode(goroslib.NodeConf{
		Name:          "goroslib_sub",
		MasterAddress: "127.0.0.1:11311",
	})
	if err != nil {
		panic(err)
	}
	defer n.Close()

	// create a subscriber
	sub, err := goroslib.NewSubscriber(goroslib.SubscriberConf{
		Node:     n,
		Topic:    "test_topic",
		Callback: func (msg *sensor_msgs.Imu) {
                        onMessage(msg, "test_topic")
                },
	})
	if err != nil {
		panic(err)
	}
	defer sub.Close()

	// freeze main loop
	select {}
}

[joao-aguizo]

Ahh perfect! That answered my question 👍 .
Thank you very much @aler9

[swarmt]

For anyone else that lands here, believe this should be:

sub, err := goroslib.NewSubscriber(goroslib.SubscriberConf{
		Node:     n,
		Topic:    "test_topic",
		Callback: func (msg *sensor_msgs.Imu) {
			onMessage(msg, "test_topic")
		},
	})