self as param, and setting scope? - lua

Question

Can someone please help me with this.
local function TestPrice()
local obj1 = require("myObj")
local obj2 = require("myObj")
obj1:setPrice(30)
obj2:setPrice(40)
print(obj1.price) -- this prints '40'. Setting price on obj2 changes the price in obj1
end
and
-- myObj.lua
local M = {
price = -1;}
local function _setPrice(self, newprice)
self.price = newprice
-- todo other stuff
end
M.setPrice = _setPrice
return M
I thought that by setting self as a param it set the scope. Why does calling this function on obj2 update the value of obj1?

Answer 1

You need a function to create new object
-- myObj.lua
local M = {}
local function _setPrice(self, newprice)
self.price = newprice
-- todo other stuff
end
M.setPrice = _setPrice
M.__index = M
local function create_new_obj()
local obj = {price = -1}
setmetatable(obj, M)
return obj
end
return create_new_obj
-- main.lua
local function TestPrice()
local obj1 = require("myObj")()
local obj2 = require("myObj")()
obj1:setPrice(30)
obj2:setPrice(40)
print(obj1.price, obj2.price)
end
TestPrice()

Answer 2

In your code require load once, and second require give you same object. You should implement some kind of copy method.
-- myObj.lua
local M = {
price = -1;}
local function _setPrice(self, newprice)
self.price = newprice
-- todo other stuff
end
function M:copy()
return {["price"] = self.price, ["setPrice"]=_setPrice, ["copy"] = self.copy}
end
M.setPrice = _setPrice
return M