OOP MVC structure binding thru interface [closed] - oop

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I'm trying to build an MVC framework with OOP style.
My idea was to bind controller & service during route session and let function accessible thru interface.
I've encounter an issue when function triggered to service level, it keep returning
"runtime error: invalid memory address or nil pointer dereference"
Route:
var (
testService service.Person = service.NewPerson()
testController controller.TestController = controller.NewTestController(testService)
)
func RouteHandler(rg *gin.RouterGroup) {
routes := rg.Group("/api")
{
routes .GET("/test", testController.Greet)
}
}
Controller:
type TestController interface {
Greet(ctx *gin.Context)
}
type testController struct {
testService service.Person
}
func NewTestController(testService service.Person) TestController {
return &testController{
testService: testService,
}
}
func (controller *testController) Greet(ctx *gin.Context) {
res := controller.testService.Greet()
fmt.Println(res)
ctx.JSON(http.StatusOK, "test")
}
Service:
type Person interface {
Greet() string
}
type person struct {
Person
}
func NewPerson() Person {
return &person{}
}
func Greet() string {
return "Hello"
}

Answer 1

Currently person service embeds the Person, but NewPerson factory method does not assign anything to the Person field, leaving it as nil. When Greet method is invoked on a person struct, the call is delegated to embedded interface Person which is nil and this causes a crash.
Assuming that the person is an "implementation" of the Person interface or more precisely the person should provide the methods with the same signature that is defined by the Person interface, the fix could be as follow:
type Person interface {
Greet() string
}
type person struct {
}
func NewPerson() Person {
return &person{}
}
func (person) Greet() string {
return "Hello"
}
It is worth mentioning that interfaces in Go are implicit. It is possible that your current person declaration is due to habits from other languages, where you have to explicitly indicate that a class (in Go there are no classes) implements some interface.