Use pointer as a function's argument

How can I use methods of function arguments?

func writeToInflux(c interface{}, host string, service string, state string) bool {
	fmt.Println(reflect.TypeOf(c), host, service)

	bp, e := client.NewBatchPoints(client.BatchPointsConfig{
		Database:  database,
		Precision: "us",
	})

	if e != nil {
		log.Print(e)
	}

	tags := map[string]string{
		"host":    host,
		"service": service,
	}

	fields := map[string]interface{}{
		"state": state,
	}

	pt, err := client.NewPoint("mon", tags, fields, time.Now())

	if err != nil {
		log.Print(err)
	}

	bp.AddPoint(pt)

	if err := c.Write(bp); err != nil {
		log.Print("write failed " + err)
	}

	return true
}

func handler(w http.ResponseWriter, r *http.Request) {
	c, err := client.NewHTTPClient(client.HTTPConfig{
		Addr:     "http://10.x.x.x:8086",
		Username: username,
		Password: password,
	})
	if err != nil {
		log.Print(err)
	}
    a := strings.Split(r.URL.Path, "/")
    writeToInflux(c, a[3], a[4], a[5])
}

In this example i can't use parameters of c variable, or maybe there is another options to use c as parameter to function?

In writeToInflux, the c interface{} doesn't specify any methods c should implement. You should use sine InfluxWriter interface so you can call c.Write:

type InfluxWriter {
    Write(bp client.BatchPoints) (*client.Response, error)
}

Alternatively, writeToInflux can accept a client.Client, giving you access to all its methods.

"c" is an interface{} type, Having an interface in function parameter, you can able to pass any struct or any data types into it.

In your case you want c to use the function write
if err := c.Write(bp); err != nil {
        log.Print("write failed " + err)
    }

The compiler doesn't know the type of c, so you need to type assert it.

Try this, It will work

newC,ok:=  c.(type of c)    type of C -> a struct or any type which has a method write

if ok {
    if err := newC.Write(bp); err != nil {
            log.Print("write failed " + err)
        }

}     

Or Change your function like this

func writeToInflux(c client.Client, host string, service string, state string) bool