golua-使用定义的方法声明lua类

Question

I'm trying to use golua package to build an extension API for my application written in Go. My idea is to have several classes exposed to lua VM, for example Book class:

local book = Book.Create("Le Petit Prince")
print(book)
book:save()

What I'm able to do now is just basic:

type Book struct {
    Id int64
    Title string
}

func BookCreate(L *lua.State) int {
    title := L.ToString(1)
    p := &Book{Id: 1, Title: title}
    L.PushGoStruct(p)
    return 1
}

func BookToString(L *lua.State) int {
    book, _ := L.ToGoStruct(1).(*Book)
    L.PushString(fmt.Sprintf("Book(Id=%d, Title=\"%s\")", book.Id, book.Title))
    return 1
}

L := lua.NewState()
defer L.Close()
L.OpenLibs()

L.NewMetaTable("Book")
L.SetMetaMethod("Create", BookCreate)
L.SetMetaMethod("tostring", BookToString)
L.SetGlobal("Book")

Which allows me to do this:

local book = Book.Create("Le Petit Prince")
print(Book.tostring(book))

But not this:

local book = Book.Create("Le Petit Prince")
print(book:tostring())

// reflect: call of reflect.Value.Type on zero Value

My questions

1. How to create lua class equivalent to one described in A Simplified Way to Declare Lua Classes?
2. How to add "magic methods" to class like __tostring here

Answer 1

I have not used go, but it looks like you never set Book as a metatable for the new book you create. Im fairly sure this does not happen automatically.

See an example I found here https://github.com/stevedonovan/luar/blob/master/luar.go#L52

What is important here is that when a userdata or any object is made (your book), you need to get the global metatable and then set it as metatable with L.SetMetaTable(-2)