Why does my Go code not run? - go

Question

package main
import (
"fmt"
"github.com/ant0ine/go-json-rest"
"net/http"
)
type App struct {
Id string
Name string
}
func GetApp(w *rest.ResponseWriter, req *rest.Request) {
user := App{
Id: req.PathParam("id"),
Name: "Antoine",
}
w.WriteJson(&user)
}
type MyResourceHandler struct {
rest.ResourceHandler
}
type ResourceController interface {
Show(w *rest.ResponseWriter, req *rest.Request)
Create(w *rest.ResponseWriter, req *rest.Request)
Update(w *rest.ResponseWriter, req *rest.Request)
Delete(w *rest.ResponseWriter, req *rest.Request)
}
func (self *MyResourceHandler) AddResource(name string, c ResourceController) error {
show_func := func(w *rest.ResponseWriter, r *rest.Request) {
c.Show(w, r)
}
create_func := func(w *rest.ResponseWriter, r *rest.Request) {
c.Create(w, r)
}
update_func := func(w *rest.ResponseWriter, r *rest.Request) {
c.Update(w, r)
}
delete_func := func(w *rest.ResponseWriter, r *rest.Request) {
c.Delete(w, r)
}
err := self.ResourceHandler.SetRoutes(
rest.Route{"GET", fmt.Sprintf("/%s/:id", name), show_func},
rest.Route{"POST", fmt.Sprintf("/%s", name), create_func},
rest.Route{"PUT", fmt.Sprintf("/%s/:id", name), update_func},
rest.Route{"DELETE", fmt.Sprintf("/%s/:id", name), delete_func},
)
return err
}
type AppController struct{}
func (self *AppController) Show(w *rest.ResponseWriter, r *rest.Request) {
app := App{
Id: r.PathParam("id"),
Name: "Antoine",
}
w.WriteJson(&app)
}
func (self *AppController) Create(w *rest.ResponseWriter, r *rest.Request) {
app := App{
Id: r.PathParam("id"),
Name: "Antoine",
}
w.WriteJson(&app)
}
func (self *AppController) Update(w *rest.ResponseWriter, r *rest.Request) {
app := App{
Id: r.PathParam("id"),
Name: "Antoine",
}
w.WriteJson(&app)
}
func (self *AppController) Delete(w *rest.ResponseWriter, r *rest.Request) {
app := App{
Id: r.PathParam("id"),
Name: "Antoine",
}
w.WriteJson(&app)
}
func main() {
handler := MyResourceHandler{}
controler := AppController{}
handler.AddResource("app", controler)
http.ListenAndServe(":9008", &handler)
}
I have implemented all of four methods of interface ResourceController, but it tells me:
./fakeapi.go:93: cannot use controler (type AppController) as type ResourceController in function argument:
AppController does not implement ResourceController (Create method requires pointer receiver)

Answer 1

It's in the error message: (Create method requires pointer receiver)
You've defined Create on *AppController (pointer to an AppController), but you're trying to use an AppController, which does not satisfy the interface.
The solution you probably want is to change controler := AppController{} to controler := &AppController{}

Answer 2

As cthom06 says, the answer is in the error.
The reason for the error message is that you have only implemented ResourceController when you are passing a pointer and not a value.
When you implemented Show, Create, etc., you used
func (self *AppController)...
This requires the method to get a pointer receiver, but AddResources is given the value of controler, not the pointer.
Here is some example code to show the problem:
package main
import "fmt"
type I interface {
Show(i int)
}
type T struct{}
func (t *T) Show(i int) {
fmt.Println(i)
}
func CallShow(i I) {
i.Show(32);
}
func main() {
obj := T{}
// CallShow(obj) // This doesn't work unless you change func (t *T) to func (t T)
CallShow(&obj) // This works because you pass a pointer
}

Answer 3

Also "ResourceHandler" is deprecated. I would recommend to use the v3 API:
api := rest.NewApi()
api.Use(rest.DefaultDevStack...)
router, err := rest.MakeRouter(
// your routes here ...
)
if err != nil {
log.Fatal(err)
}
api.SetApp(router)
log.Fatal(http.ListenAndServe(":8080", api.MakeHandler()))
Antoine - go-json-rest author