package flash

import (
    "encoding/gob"
    "fmt"
    "net/http"
    "os"

    "github.com/gorilla/sessions"
)

const (
    // TicketBox holds the ticket cookie name.
    TicketBox = "ticket"
)

var (
    // Store holds all session data.
    Store = sessions.NewCookieStore([]byte(os.Getenv("SESSION_KEY")))
)

type Message struct {
    Type    string
    Content string
}

type M map[string]interface{}

func init() {

    gob.Register(&Message{})
    gob.Register(&M{})
}

// Add creates a new flash message.
func Add(w http.ResponseWriter, r *http.Request, box string, content Message) error {
    // Get a session.
    session, err := Store.Get(r, box)
    if err != nil {
        return err
    }
    // Set a new flash.
    session.AddFlash(content)
    session.Save(r, w)

    return err
}

// Get retrieves saved flash messages.
func Get(w http.ResponseWriter, r *http.Request, box string) ([]interface{}, error) {
    // Get a session.
    session, err := Store.Get(r, box)

    // Get the previous flashes, if any.
    if flashes := session.Flashes(); len(flashes) > 0 {
        // Use the flash values.
        session.Save(r, w)
        return flashes, err
    }

    return []interface{}{}, err
}

// Add flash message
if err := flash.Add(w, r, flash.TicketBox, flash.Message{Type: "111", Content: "222"}); err != nil {
    http.Error(w, "Could not save flash message", http.StatusInternalServerError)
    return
}

if session, err := flash.Get(w, r, flash.TicketBox); err != nil {
    http.Error(w, err.Error(), http.StatusInternalServerError)
    return
} else {
    td["Flashes"] = session
}

fmt.Println(td["Flashes"])

if message, ok := td["Flashes"].(*[]flash.Message); !ok {
    // Handle the case that it's not an expected type
    fmt.Println(ok)
} else {
    // message
    fmt.Println(message)
}

[0xc0000d9740]
false