Can someone explain metatables and metamethods to me. Not sure I understand fully

[quasi meadow]

Title

https://create.roblox.com/docs/luau/metatables

https://www.youtube.com/watch?v=bk8UVm-gxBs

[tulip shard]

metatables are just tables containing information about another table

they can also function as tables, which allows you to mimic OOP

[subtle hinge]

it basically gives more functionality to a table, which allows you to do epic stuff with them (such as OOP)

the metatable is just a table with all functions inside of it.
those functions are called methamethods

it basicly allows you to do stuff like, subtract tables from eachother. (__sub)

is there anything you specificly don't understand of them?

[tulip shard]

when you do setMetatable(table param, table param) you are saying that the table in paramater two will be a metatable for table in parameter one

[mystic sundial]

local myMetatable = {} -- a normal table

local myTable = {} -- a normal table

setmetatable(myTable, metatable) -- sets myMetatable to be myTables metatable

[tulip shard]

table will index metatable for metamethods when certain events occur, like when you index table but there is no relevant key (but there is an __index key/pair in ur metatable)

[mystic sundial]

local myMetatable = {} -- a normal table

-- if this table is a metatable then lua will use this tables __index key to know what to do when we access a key in the parent table
myMetatable.__index = function(...) print(...) end 


local myTable = {} -- a normal table

setmetatable(myTable, metatable) -- sets myMetatable to be myTables metatable

[quasi meadow]

From the tutorial and the Curve tutorial, I only grasped that metatables connect 2 tables together. When the main table didn't have a value, when you would index the code for it: the metatable would fill in for it

[subtle hinge]

thats the __index function

thats why modules are like this

[quasi meadow]

https://www.youtube.com/watch?v=TJsL04R84tw

[subtle hinge]

local Module = {}
Module.__index = Module

Module.Hello = "hi"

function Module.new()
    local self = setmetatable({},Module)
    
    -- self does not have the index Hello, so it will check the metatable, which has the index function, which will return the table module, which has hello, so it returns "hi"
    print(self.Hello) --> expected output: "hi"

    return self
end

return Module

[quasi meadow]

Could you explain the __index more?

[subtle hinge]

basicly this works that if it can't find it in the returned value ({}) then it will see that it has a metatable (Module) and then it will return any other function FROM Module

or index

[mystic sundial]

local myMetatable = {} -- a normal table

-- if this table is a metatable then lua will use this tables __add key to know what to do when we try to add to the parent table
myMetatable.__add = function(...) print(...) end 


local myTable = {} -- a normal table

setmetatable(myTable, metatable) -- sets myMetatable to be myTables metatable

myTable + 5 -- when we try to add to a table it will call the __add function

[tulip shard]

if your table as a metatable with __index it will reference whatever you set it equal to when table is indexed but there is no key

[quasi meadow]

local shrug = {
[0] = "red",
"blue",
"green",
nil,
"orange"
}

local metathis = {}

setmetatable(shrug, metathis)
print(shrug[3])

?

this will print nil

yes?

[subtle hinge]

I've updated this code

[quasi meadow]

so what exactly is the metatable doing?

[rancid anchor]

think of it like a table that stores functions

[mystic sundial]

in your example nothing

[ripe carbon]

It's like a power

[subtle hinge]

updated it again

[ripe carbon]

A power for tables

[quasi meadow]

oh

actually that perfectly explains it

[rancid anchor]

those functions are metamethods

[subtle hinge]

i litterly said that lol

[subtle hinge]

in this message

[mystic sundial]

https://create.roblox.com/docs/luau/metatables

you can find all the metamethods here

[quasi meadow]

So all these metamethods have specific uses that ill have to look up in order to use and learn about

neat

[rancid anchor]

yea

[quasi meadow]

i posted that first thing lol

[quasi meadow]

kind of hard to keep track with 5 people trying to help at once lmao

sorry

[mystic sundial]

https://tenor.com/view/youre-a-big-star-now-big-s-tar-now-celebrity-mark-wahlberg-gif-4735565

[quasi meadow]

would you consider it to sort of be like matrixes in precalculus?

[subtle hinge]

true

[rancid anchor]

i'm not in precalc yet

i take it next year

[quasi meadow]

let me explain it like this:

[rancid anchor]

errrrrrrrrrrrrrrrr

[quasi meadow]

matrices are tables with a certain number of x and y values. You can do math with them like multiplication and whatnot

an example:

[rancid anchor]

oh i see

[quasi meadow]

now, if I am understanding this right... metatables are SORT OF similar?

except instead of multiple positions, its only the table itself

[rancid anchor]

pretty much yea

[quasi meadow]

okay yeah then that explains everything

[rancid anchor]

you could do this with the _add metamethod

so yea ig so

[mystic sundial]

Tables and matrices have nothing to do with each other

[quasi meadow]

._.

[mystic sundial]

Metatables don't do anything out of the box

They do no math

[quasi meadow]

._ .

i know.

I was not saying they have anything to do with each other

i was making a comparison

[rancid anchor]

the math-related metamethods could do that

[mystic sundial]

I don't get the comparison

[quasi meadow]

not saying they are similar

[quasi meadow]

have 2 tables

do stuff to the table with other table

Regardless. I understand it way better now.

[mystic sundial]

They don't do stuff with each other

The metastable is like a list of settings for the first table

Metatable does nothing just holds the settings

[quasi meadow]

even still.

The commparison helped me to expand my knowledge, and while they aren't inherently similar. It DOES help me in this case to know.

I'm not saying it's logical Suphi. I'm saying it's making a comparison to understand

[mystic sundial]

But are you sure what you know is correct

[quasi meadow]

not a comparison as in a logical one

[mystic sundial]

If I told you do make something with metatables could you do it?

[quasi meadow]

I mean yeah I think I have like 30% more understanding now than I did before.

[rancid anchor]

only one way to find out

[quasi meadow]

Which in my opinion, is way better than the 5% I had before.

[rancid anchor]

go make something using metatables @quasi meadow

[mystic sundial]

local value = 0

local myTable = {}

myTable + 5 -- make it so that when I add 5 it adds 1 to value and prints it

[quasi meadow]

local value = 0
local times = 3

local myTable = {}
local metathismetathathaveyoueverevenmetagirlbefore = {
    __call = function(five, val2)
        for i, numbers in ipairs(five) do
            local multi = numbers/5 
            value += 1 * multi --1*1, 1*2, 1*3; added together = 6
        end
        return value
    end
}

task.wait(3)

for i = 1, times, 1 do
    table.insert(myTable, 5 * i)
    --print(myTable) --{5, 10, 15}
end

local itstimetoddddddddddddduel = setmetatable(myTable, metathismetathathaveyoueverevenmetagirlbefore)
print(itstimetoddddddddddddduel(myTable))```

[quasi meadow]

?

"make it so that when I add 5, it adds 1 to value and prints it"

makes it so when you add exactly 5, it adds 1 value. Values in increment of 5 add additional value corresponding to the multitude of 5

the code itself works Suphi.

[mystic sundial]

When you do

Mytable + 5

It should add 1 to value

[quasi meadow]

Then why don't you show me then.

I said I have roughly a 35% understanding of it.

Never said I could do anything with a 35% understanding

[tulip shard]

maybe there is a metamethod that fires when you do table + something ? 🙂

[mystic sundial]

#1172253240478400542 message

I already showed you most of it

[quasi meadow]

I was trying to use the documentation.

Also I despise surprises.

Im asking you to show me.

Not to redirect me and give me more hints

[mystic sundial]

Did you run the code I showed above

[quasi meadow]

The video on metatables has a high pitched ringing that kills my ears, nor does this help me specifically

[mystic sundial]

I think it's ok to ignore that error

Make sure you type metatable correctly

[quasi meadow]

I copy pasted your code.

this is it with the right variable names

[mystic sundial]

Ok and what's it print when you run it

[quasi meadow]

Hold on my boyfriend is snoring. Give me a moment

[mystic sundial]

Good now what did you learn

[quasi meadow]

absolutely nothing

[mystic sundial]

Ok change 5 to 8

[quasi meadow]

why did it print {} THEN the 5

[mystic sundial]

And run it again

[quasi meadow]

and why is myTable += 5 printing in the output without a print statement
~~yes I was blind ~~

actually no

[mystic sundial]

This is where you need to connect the dots

[quasi meadow]

scratch that

i see it.

still doesnt explain the {} then the 5

[mystic sundial]

Can you make it print {} 8

[quasi meadow]

i mean yeah

you just change the 5 to an 8

[mystic sundial]

Ok

Put something inside mytable

Like random value

What's it print now

[quasi meadow]

Im going to assume it's going to add the 8 to the value.

[mystic sundial]

No

[quasi meadow]

?

ill try it then

[mystic sundial]

Metatables don't do anything

[quasi meadow]

:T

[mystic sundial]

Ok what did you learn

[quasi meadow]

what i already knew before

[mystic sundial]

What's that

Nothing

[quasi meadow]

?

what do you mean nothing

[mystic sundial]

Ok first question

Why is it printing

[quasi meadow]

line 5.

[mystic sundial]

Ok

Do you know what ... Is

[quasi meadow]

you are setting the __add of the metatable to print whatever ... is, so in this case I'm assuming you are wanting to print what you add to MyTable. However this does not add to the MyTable itself just yet. Instead, you are printing it next to MyTable

I've seen ... here and there, but unfortunately: no. I do not.

[mystic sundial]

Think of ... Like a list of values

A little like a table

Change ... To a, b, c

And print a,b,c

[quasi meadow]

? im going to guess it will print the table, 8, then nil

[mystic sundial]

Yes

[quasi meadow]

actually nvm

itwont print anything at all

xD

but thats because i need to update the function(...)

[mystic sundial]

Yes

[quasi meadow]

before I look at studio

Im going to guess it will look like

{5} 8 nil

[mystic sundial]

Ok so what's happening

[quasi meadow]

a is the table, b is the value we are attempting to add, and c has no variable associated with it. So it is nil

[mystic sundial]

Ok now do

Mytable + "hello"

Or maybe that won't work

[quasi meadow]

but we haven't made a __concat?

[mystic sundial]

Concat is ..

Not +

[quasi meadow]

e

oh

i was not expecting that

[mystic sundial]

It worked

[quasi meadow]

i mean i guess it's because nothign is being added to the table just yet so it still does make logical sense

[mystic sundial]

Ok so we know that if we do
Mytable + anyvalue

It will call the function inside the metastable

[quasi meadow]

hmm

[mystic sundial]

And that function will tell us the table and the value we tried to add

[quasi meadow]

I see.

So you want to check if b == 5 then add 1 to value then return value?

[mystic sundial]

So how could we make it so that if we add 5 it adds 1 to value

We don't have to return anything

[quasi meadow]

oh

is the first part correct at least?

[mystic sundial]

local newValue = mytable + 5

What do you think newvalue will be

[quasi meadow]

{} 5 ?

[mystic sundial]

Nope

[quasi meadow]

hm

[mystic sundial]

It's nil

[quasi meadow]

yes..

I wonder why it is nil

[mystic sundial]

Ok now return a random value inside the function

For instance return "bob"

[quasi meadow]

nil

wait a sec

[mystic sundial]

Nope

[quasi meadow]

it doesnt return anything

[mystic sundial]

Mytable + anyvalue should now be equal to bob

Print(Mytable + anyvalue) will print bob

[quasi meadow]

huh.

ah

i see

[mystic sundial]

Not +=

[quasi meadow]

yeah i got that bit.

I got the error after I changed it to only +

[mystic sundial]

Also

[mystic sundial]

You did += above

[quasi meadow]

ahhhhhh

okay

I see.

[mystic sundial]

That will set my table to bob

[quasi meadow]

I think this is why

but

i think its because it's not followed by anything

[mystic sundial]

You can ignore the error

[quasi meadow]

the print is fine

yes it prints bob :)

[mystic sundial]

What you do mytable += 5 it's like doing mytable = mytable + 5

[quasi meadow]

yes

[mystic sundial]

Ok

[quasi meadow]

I believe I was just trying to finish the statement so I found += worked

but print(myTable + 5) works as you were saying

[mystic sundial]

So hopefully if you followed along and understood everything you should be at 80% understanding

[quasi meadow]

Yeah.

So far I think so.

[mystic sundial]

So you can see why metatables are very powerful and can do many things

[quasi meadow]

I can't see it just yet unfortunately

But I can try to imagine systems I might use for it..

[mystic sundial]

When you do

[quasi meadow]

Like maybe an economy system?

[mystic sundial]

Vector3 + vector3

Or when you do vector3 * 2

Now you know how Roblox makes that work

[quasi meadow]

hhahaaha

ahaha

Vector3.new(Vector3.X * 2, Vector3.Y * 2, Vector3.Z * 2)

[mystic sundial]

Vector3 is just a table with a metatable

[quasi meadow]

/jk

Im going to try and research __index now

😃

[mystic sundial]

Maybe if you watch my video a second time it might be easier to understand now

[quasi meadow]

potentially.

I will say I was partially right in my earlier comparison

it is like matrices, except it's allowing the matrices to be calculated with what you do with it

and the meta table is the math you want to do. Holding the important bits and pieces around what you do when you want to do the math

Yeah I can understand the video now

I dont understand when and where I apply index yet though

[woeful zodiac]

I’d say matrices are over complicating things tbh (as a non mather)

[quasi meadow]

maybe

one might say metatables are more like "tables with functions inside of them" xD

as a comparison

[woeful zodiac]

Basically

[quasi meadow]

I cant think of a use just yet which is unfortunate

i retain information better when I can apply it

[woeful zodiac]

Proxy tables ig

[quasi meadow]

but ty father the hairy balls have bestowed on me divine vision and have helped me immensely @mystic sundial

[woeful zodiac]

😧

[quasi meadow]

https://tenor.com/view/монах-monk-gif-14891465

[quasi meadow]

?

[woeful zodiac]

https://discord.com/channels/909926338801061961/1171833528779018281

[quasi meadow]

gotcha

i see

i think

:)

I guess its an anticheat thing?

[woeful zodiac]

No

The term proxy should explain alot

[quasi meadow]

i mean i guess

[acoustic river]

basically metatables is this

[quasi meadow]

ah i see

brilliant

[acoustic river]

yup

[acoustic river]

ok a simpler way to look at it is just think of them like roblox functions

like part.Touched

similarly table.__'metamethod here' will fire

👍

[quasi meadow]

yeah i get it now lol

suphi hand held me threw it

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