Lua 个对象不唯一

Question

在尝试创建一个非常简单的 class 继承时，所有对象似乎都共享相同的值

这是我的代码的简化：

--Generic class
Object = {}

function Object:new (type,id,name)
  o = {}
  self.type = type or "none"
  self.id = id or 0
  self.name = name or "noname"
  self.direction = "down"
  self.animations = {}
  self.animations.stack = {}
  self.animations.idle = {}
  self.animations.idle[self.direction] = {}
  setmetatable(o, self)
  self.__index = self
  return o
end

function Object:draw(x,y)
  local img = self.animations.idle["down"][0]
  print("drawing " ..self.name.." as "..img)
end

function Object:setimg(img)
  self.animations.idle["down"][0] = img
end

Player = Object:new()

-- Player class
function Player:new(id,name)
  local o = self

  o.id = id or 0
  o.name = name or "noname"

  o.collision = {}
  o.collision.type = "player"

  return o
end

function Player:move(x,y)
  print("moving to ",x,y)
end

-- Testing
blockimg = "block.png"
grassimg = "grass.png"
plyrimg = "player.png"

block = Object:new("solid",1,"block")
block:setimg(blockimg)

grass = Object:new("floor",3,"grass")
grass:setimg(grassimg)

player = Player:new(1, "plyr1")
player:setimg(plyrimg)

block:draw() -- >drawing grass as player.png
grass:draw() -- >drawing grass as player.png
player:draw()-- >drawing plyr1 as player.png

由于 player:setimg 是最后调用的，所有 "objects" 都以 plyrimg 结束，所以它们不是唯一的

Answer 1

每次创建新对象实例时，此函数都会创建或覆盖共享对象的属性table。

function Object:new (type,id,name)
  o = {}
  self.type = type or "none"
  self.id = id or 0
  self.name = name or "noname"
  self.direction = "down"
  self.animations = {}
  self.animations.stack = {}
  self.animations.idle = {}
  self.animations.idle[self.direction] = {}
  setmetatable(o, self)
  self.__index = self
  return o
end

如果您希望它们是唯一的，则需要在每个新实例上创建这些属性。否则，Object:setimg 将查找索引链以找到 animations，并将图像放在共享属性.

中

function Object:new (type,id,name)
  local o = {}
  -- ...
  o.animations = {} -- Or in Player:new
  -- ...
  self.__index = self
  return setmetatable(o, self)
end

Answer 2

如果不将 self 传递给构造函数，则可以避免很多问题。我通常这样定义 classes：

local class={x=0,y=0}
local _class={__index=Class}
-- I like prefixing metatables with _, but that's just a personal thing
class.new(x, y)
  return setmetatable({x=x, y=y}, _class)
end
class:print() print(self.x, self.y) end
class.sub(sub) return getmetatable(sub)==_class end

这是假设 class 在它自己的文件中或在 do 块中，以保持局部变量对除 class 及其闭包之外的任何东西隐藏。

您可以在 github 上的 lua 文档中阅读更多相关信息。

Lua 个对象不唯一

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