How to split the interface passed to the method

I use this library tucnak/telebot to build a telegram bot.

Method b.Handle() have two parameters such as Handle(endpoint interface{}, handler interface{})`.

Here is the code i use for a starter

func main() {
	b, err := tb.NewBot(tb.Settings{
		Token:  "TOKEN_HERE",
		Poller: &tb.LongPoller{Timeout: 10 * time.Second},
	})

	if err != nil {
		log.Fatal(err)
		return
	}
    // i want to split this(interface)
	b.Handle("/hello", func(m *tb.Message) {
		b.Send(m.Sender, "Hello World!")
	})

	b.Start()
}

Here is what I have tried to compile :

func main() {
	b, err := tb.NewBot(tb.Settings{
		Token:  "TOKEN_HERE",
		Poller: &tb.LongPoller{Timeout: 10 * time.Second},
	})

	if err != nil {
		log.Fatal(err)
		return
	}
                    
	b.Handle("/hello", handleHello(b))

	b.Start()
}

func handleHello(b *tb.Bot) {
		b.Send(m.Sender, "Hello World!")
}

I have an error with this code : undefined m, in m.Sender() and I can't use m as a parameter for that function call, because of the same error. I don't understand where that m comes from.

The bot responsibility is to listen some sockets, whatever, and calls your function handlers when a message arrives on the associated path handler.

Thus, you should not try to call your handlers like in b.Handle("/hello", handleHello(b)). Instead pass the function handler to the bot b.Handle("/hello", handleHello). Let the bot call that function with the new message as a parameter like in func(m *tb.Message).

To retain a reference to b, you can proceed as described by Sinan Coment. Write a function that takes in parameter the bot and returns a function that receives the message as a parameter.

The bot instance b acts as a muxer, you can re use that terminology to improve the meaning of your code.

A muxer is defined as [...] a request multiplexer. It matches the URL of each incoming request against a list of registered patterns and calls the handler for the pattern that most closely matches the URL.

Though, I want to suggest you to wrap that instance of telebot.Bot into a type that defines message handlers as methods.

package main

import (
	"log"
	"time"

	tb "gopkg.in/tucnak/telebot.v2"
)

func main() {
	mux, err := tb.NewBot(tb.Settings{
		Token:  "TOKEN_HERE",
		Poller: &tb.LongPoller{Timeout: 10 * time.Second},
	})

	if err != nil {
		log.Fatal(err)
		return
	}

	bot := botHandlers{Bot: mux}

	mux.Handle("/hello", bot.handleHello)

	mux.Start()
}

type botHandlers struct {
	*tb.Bot
}

func (b botHandlers) handleHello(m *tb.Message) {
	b.Send(m.Sender, "Hello World!")
}

https://play.golang.org/p/6ng6WSIp8Er

As you can see hello handler takes a parameter called m here.

b.Handle("/hello", func(m *tb.Message) {

so you should return a function that takes the same parameter.

func handleHello(b *tb.Bot) func(m *tb.Message) {
    return func(m *tb.Message) {
	    b.Send(m.Sender, "Hello World!")
    }
}