自我作為參數，並設置範圍？ (self as param, and setting scope?)

問題描述

自我作為參數，並設置範圍？ (self as param, and setting scope?)

有人可以幫我解決這個問題嗎？

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

和

‑‑ myObj.lua
local M = {
price = ‑1;}

local function _setPrice(self, newprice)
  self.price = newprice
  ‑‑ todo other stuff
end

M.setPrice = _setPrice

return M

我認為通過將 self 設置為參數來設置範圍。為什麼在obj2上調用這個函數會更新obj1的值？

參考解法

方法 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()

方法 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

(by ausgeorge、Egor Skriptunoff、Leszek Mazur)

參考文件

1. self as param, and setting scope? (CC BY‑SA 2.5/3.0/4.0)