Casting an "alert" type in libtorrent, using Golang bindings

I am developing a personal project in Golang, using libtorrent-go

When I do receive an alert of type "save_resume_data_alert", I pick it up and have to CAST it as written in libtorrent documentation

...
        save_resume_data_alert const* rd = alert_cast<save_resume_data_alert>(a);
...

But i really have not idea how to cast it in golang! Current code:

package main

import (
	lt "github.com/steeve/libtorrent-go"

	"log"
	"time"
)

func main() {

	randomTorrent := lt.NewAdd_torrent_params()
	randomTorrent.SetUrl("PUT A MAGNET LINK HERE")
	randomTorrent.SetSave_path(".")

	ec := lt.NewError_code()
	torrentSession := lt.NewSession()
	torrentSession.Set_alert_mask(status_notification + storage_notification)
	torrentSession.Listen_on(lt.NewStd_pair_int_int(6900, 6999), ec)
	if ec.Value() != 0 {
		log.Println(ec.Message())
	}

	torrentHandle := torrentSession.Add_torrent(randomTorrent, ec)
	if ec.Value() != 0 {
		log.Println(ec.Message())
	}

	go func() {
		for {
			if torrentSession.Wait_for_alert(lt.Seconds(10)).Swigcptr() == 0 {
				log.Println("Alert timeout occurred!")
			}

			alert := torrentSession.Pop_alert()
			switch alert.What() {
			default:
				log.Printf("Alert: %#v", alert.What())
			case "metadata_received_alert":
				log.Println("Received Metadata!! finally!")
				torrentHandle.Save_resume_data()
			case "save_resume_data_alert":
				log.Println("Wrote Metadata!")
				// need to actually write the resume_data :( can't find how
			case "save_resume_data_failed_alert":
				log.Println("Failed Metadata!")
			}
		}
	}()

	select {}
}

As stated above, libtorrent-go developer answered me, so I am forwarding the answer for posterity reasons.

Casting C++ structures in Golang using SWIG library is documented in SWIG-Golang documentation.
In particular in this statement:

> Given a value of the interface type, Go code can retrieve the pointer
> to the C++ type by calling the Swigcptr method. This will return a
> value of type SwigcptrClassName, which is just a name for uintptr. A
> Go type conversion can be used to convert this value to a different
> C++ type, but note that this conversion will not be type checked and
> is essentially equivalent to reinterpret_cast. This should only be
> used for very special cases, such as where C++ would use a
> dynamic_cast.

In that particular piece of code I posted above, the following was necessary to make it work:

case "save_resume_data_alert":
  log.Println("Wrote Metadata!")
  // need to actually write the resume_data :( can't find how
  SaveRDAlert := lt.SwigcptrSave_resume_data_alert(alert.Swigcptr())
  log.Printf("Resume Data: %#v", SaveRDAlert.GetResume_data())