I have the next code and I'm trying to create a copy of the object Test:
local Test = {} do
local var1, var2 = {}
function Test:Init(val1, val2, val3)
var1.val1 = val1
var1.val2 = val2
var1.val3 = val3
end
function Test:Print()
print(var1.val1)
print(var1.val2)
print(var1.val3)
end
function Test:New(obj)
obj = obj or {}
setmetatable(obj, self)
self.__index = self
return obj
end
end
Then I'm creating my objects like this:
local obj1 = Test:New()
obj1:Init('a','b','c')
local obj2 = Test:New()
obj2:Init('c','d','e')
obj1:Print()
obj2:Print()
The result will be this:
c, d, e
c, d, e
As you can see the method New is not cloning correctly the object and is sharing the same instance. What am I doing wrong? I haven't cloned an object before and I'm having issues to understand how to do it.
I got that code from here: https://www.lua.org/pil/16.2.html
Thanks.
The problem occurs because you are just changing local variables, not the object itself.
When you do local Test = {} do you are not doing too much about the Test object, you are just creating the table and then creating a new scope which will be executed immediately, and inside this scope you have the variable var1, which will be shared through the scope, not the object.
The correct way to implement variables for each is actually creating fields on it:
local Test = {} do
function Test:Init(val1, val2, val3)
self.val1 = val1
self.val2 = val2
self.val3 = val3
end
function Test:Print()
print(self.val1)
print(self.val2)
print(self.val3)
end
function Test:New(obj)
obj = obj or {}
setmetatable(obj, self)
self.__index = self
return obj
end
end
Anyway setmetatable it's not about cloning objects, it implement shared behaviors and then you can create as many objects you want with those behaviors.
Related
I want to inherit method "GetName" or other methods from "Create" for "CreateInherited" and i want save unique methods from "CreateInherited" (like "GetInheritName"), but i dont know how.
My test code:
local MainTbl = {}
function MainTbl:Create(name)
local tbl = {}
tbl.name = name or 'Null'
function tbl:GetName()
return self.name
end
setmetatable(tbl, self)
self.__index = self
return tbl
end
function MainTbl:CreateInherited(name)
local tbl = {}
tbl.name = name or 'Null'
function tbl:GetInheritName()
return self.name
end
setmetatable(tbl, self)
self.__index = self
return tbl
end
local Man = MainTbl:Create('Man')
local Woman = MainTbl:CreateInherited('Woman')
print(Man:GetName())
print(Woman:GetName())
print(Woman:GetInheritName())
If I understand you, you're trying to put two different constructors into a single class. Notice that Create does most of the work that CreateInherited needs to do, so you can save yourself a lot of repeated code by calling Create inside CreateInherited. Instead of starting with an empty table, you can start with a fully formed instance from Create and add a method to it.
function MainTbl:CreateInherited(name)
local tbl = self:Create(name)
function tbl:GetInheritName()
return self.name
end
return tbl
end
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?
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()
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
in Lua we do OO programming like this:
MyClass = {}
function MyClass:new()
local obj = {}
setmetatable(obj, self)
self.__index = self
obj.hello = "hello world"
return obj
end
function MyClass:sayHi()
print(self.hello)
end
function main()
local obj = MyClass:new()
obj:sayHi()
end
When working with more compelx stuff, usually I take advantage of Lua's metamethods to proxy function calls and do whatever I need with it, like arguments parsing etc, by adding this:
MyClassMeta = {}
function MyClassMeta.__index(obj, funcName)
return function (self, ...)
//do some stuff
print("you called " .. funcName .. " with args", ...)
end
end
and changing the line:
setmetatable(obj, self)
to:
setmetatable(obj, MyClassMeta)
every function I call with an instance of MyClass will execute the code implemented in MyClassMeta.__index metamethod.
What I want to do now is inherit the MyClass existing methods, and execute MyClassMeta.__index only for functions that are not part of MyClass.
In the above example, the code will always execute the MyClassMeta.__index metamethod even when calling MyClass:sayHi():
function main()
local obj = MyClass:new()
obj:sayHi("hello")
end
you called sayHi with args hello
When you set __index to a table, it will look for properties on that table and return them if they don't exist on the instance. Since sayHi exists on the MyClass table it is used.
self.__index = self
When you set __index to a function, it can return anything for properties that don't exist on the instance. You can check if the key exists on the MyClass table and return it, then do something else if it doesn't:
MyClass = {}
MyMetatable = {
__index = function(obj, key)
if MyClass[key] ~= nil then return MyClass[key] end
return function(self, ...)
print("you called "..tostring(key))
print(" self.hello is '"..tostring(self.hello).."'")
print(" with args", ...)
end
end
}
function MyClass:new()
local obj = {}
setmetatable(obj, MyMetatable)
obj.hello = "hello world"
return obj
end
function MyClass:sayHi()
print(self.hello)
end
function main()
local obj = MyClass:new()
obj:sayHi()
end
local obj = MyClass:new()
obj:sayHi("hello")
obj:somethingElse(1, 2, 3)
Version with Egor's comment
MyClass = {}
setmetatable(MyClass, {
-- if it's not found on MyClass, return a function
__index = function(self, funcName)
return function(self, ...)
print("you called "..funcName.." with args", ...)
end
end
})
function MyClass:new()
local obj = {}
-- if it's not found on obj, try self (MyClass)
setmetatable(obj, { __index = self })
obj.hello = "hello world"
return obj
end
function MyClass:sayHi()
print(self.hello)
end
local obj = MyClass:new()
obj:sayHi()
obj:somethingElse(1, 2, 3)
When creating an object this sets the __index of the new object's metatable to MyClass, and MyClass's metatable's index to the function that is a fallback. So if the property isn't on your object or on MyClass, it will use the fallback.
As I understand lua don't call __index unless the key wasn't found in the table so I have that code and it suffers from infinite recursion in the __index part which I don't get as both values used inside the __index function already exist in the table!?
This is basically a test script for trying to save the size of the table in a memory to retreive when # is called
do
local lenKey,originalKey = {},{}
fastKey = {}
fastKey.__len = function(t) return t[lenKey] end
fastKey.__index = function (t,k)
t[lenKey] = t[lenKey] +1
return t[oroginalKey][k]
end
fastKey.__newindex = function(t,k,v) t[originalKey][k] = v end
fastKey.__pairs = function ()
return function (t, k)
return next(t[oroginalKey], k)
end
end
function fastLen(t)
local proxy = {}
local c = 0
for _ in pairs(t) do
c=c+1
end
proxy[lenKey] = c
proxy[originalKey] = t
setmetatable(proxy,fastKey)
return proxy
end
end
n = fastLen{1,2,3,x=5}
--n:insert(1) -- here the __index is called and gets stackoverflow
print(#n)
You've got two typos in there: both the __index and __pairs functions contain oroginalKey instead of originalKey.
I have implemented OOP in my lua environment but it doesnt seem to be working.
I think it has something to do with how i am handling the __index and my improper use of require and module but I'm not 100% sure.
Here is the code:
Class = function( prototype )
local derived = {}
local derivedMT = {
--When indexing into a derived class, check the base class as well
__index = prototype,
--When invoking a class, return an instance
__call = function( proto, ... )
local instance = {}
local instanceMT = {
--When indexing into an instance, check the class hierarchy as well.
__index = derived,
--Calling instances is a no-no!
__call = function()
print( "WARNING! Attempt to invoke an instance of a class!" )
print( debug.traceback() )
return instance
end,
}
setmetatable( instance, instanceMT )
if ( instance.__constructor ) then
instance:__constructor( ... )
end
return instance
end,
}
setmetatable( derived, derivedMT )
return derived
end
And here is how I use it, the nil reference is a call to a base class function, that is the error/problem im having is it seems like the base class isn't being referenced.
require "Core.Camera.FreeCamera"
local T = Core.Camera.FreeCamera.FreeCamera(0,0,-35)
c = T:getObjectType() -- nil reference
print(c .." --Type" )
and here is Camera.lua the base class
local _G = _G
module(...)
local M = _G.Class()
Camera = M
function M:__constructor(x,y,z) --This never gets called.
--self.Active = false
--self.x = x
--self.y = y
--self.z = z
--self.ID = EngineManager:getCamera()
print("InCameraInstance_-_-_-_-_-__-_--_-__-_-_-_--_-_-_-_-_--_-_-_--_--__-_---_--_---__-")
end
function M:getObjectType()
return "camera"
end
And Finally Free Camera which attempts to inherit Camera.
local require = require
local _G = _G
module(...)
require "Core.Camera.Camera"
local M = _G.Class( _G.Core.Camera.Camera ) --Gross, lame might be the culprit
FreeCamera = M
function M:__constructor(x,y,z) ---WHOOPS, this does get called... the other one doesnt
self.Active = false
self.x = x
self.y = y
self.z = z
self.ID = _G.EngineManager:getCamera()
--_G.print("got Id of:" .. self.ID)
self:setCameraPosition(x, y, z, self.ID)
_G.print("<<<Camera in lua>>>")
end
I'm running out of ideas. any help would be appreciated.
Instead of:
local M = _G.Class( _G.Core.Camera.Camera )
you need to have:
local M = _G.Class( _G.Core.Camera.Camera.Camera )
First Camera is the directory name, second is the module name, third is the class name.
Edit: You can clean it up a bit like this:
local CameraModule = require "Core.Camera.Camera"
local M = _G.Class( CameraModule.Camera )