What situations should i use __index in modules and stuff

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#1

currently learning what __index does and i dont exactly get why people do stuff like

local module = {}
module.__index = module

return module

Anyways besides that, i dont see a use currently on why they are being used, so im just wondering in what situations should they be used and why

#2

Require that module and attempt to index any key, see what happens.

1 Like
#3

You can check out this post. Make sure to look through others posts before posting since it’s essentially the same topic. What does table.__index = table do?

1 Like
#4

ok yeah but like where do i use this in scripting? as in whats the point in using it

also still dont entirely get it thought this would work

local module = {}
module.__index = module

function module.new()
	local T = {}
	
	function T:One()
		return 2
	end
	
	return setmetatable(T, module)
end

function module:one()
	return 1
end

return module

(i thought it would print 2 but it didnt)

#5

wdym by any key? just something random or

#6

__index is a meta method, used along side meta tables for OOP (Object Oriented Programming) for Lua (and Luau/Roblox’s version of Lua). You really won’t use it unless you use OOP, I suggest following this tutorial for OOP on Roblox:

4 Likes
#7

Ill definitely check it out :+1:

#8 
local t = {}
setmetatable(t, {__index = t})
print(t.k)
1 Like
#9

Tried pasting it in and got
Workspace.Script:10: loop in gettable
this is spose to just be in a normal script right?

#10

It’s supposed to cause an exception, which is what you encountered.

#11

so is that bad or good?
Not sure what im spose to be getting from this

#12

You maybe forgot local _index = module

local module = {}
local _index = module
module.__index = module -- you can be rid of that.

return module
#13

That’s bad, the table’s metatable’s ‘__index’ metamethod is instructing the the table to look within itself for the indexed key, as the key doesn’t exist (is absent) for the table a cycle of table queries occurs.

#14

Is this a better method to use instead of .__index?

Oh, ok so how would i advoid doing this? do i just not set normal tables’s metatables to themselves and just do it for modules or?

#15

Yeah, you would just avoid employing a practice I demonstrated, i.e; making the table’s __index or __newindex metamethods point/refer to the table itself.

#16

read through this, not entirely sure if this is how they work but did something like this

local Block = {}
Block.__index = Block

function Block.New()
	local blockT = {}
	local B = Instance.new("Part")
	B.Size = Vector3.new(4,4,4)
	blockT["Block"] = B
	setmetatable(blockT, Block)
	
	return blockT
end

function Block:Create()
	local B = self.Block
	B.Parent = workspace
	B.Position = Vector3.new(0,0,0)
end


return Block

local mod = game.ServerScriptService.ModuleScript
local BlockMod = require(mod)

local D = BlockMod.New()

D:Create()
#17

ok, i get what you are saying, but just to be careful i can a modules metatable to itself right?

#18

Hey I just found something only covering metatables and metamethods (and as I mentioned before __index is a metamethod) I am currently reading it aswell, and it is really doing a great job at explaining, here:

@simplyjustbased

#19

It should do that. The reason your code didn’t do that was because you capitalized one of the functions, which meant they were different.

#20

oh, i just saw that thanks for pointing it out