How to run code if a property is changed?

Help and Feedback Scripting Support
,
#1

Suppose I got something like this

local Gun = {}
Gun.__index = Gun

function Gun.new(gunInstance, owner, enabled)
	local metaData = {}
	setmetatable(metaData, Gun)
	
	metaData.Model = gunInstance
	metaData.Owner = owner
	metaData.Enabled = enabled
	
	return metaData
end

return Gun

I need code to run when .Enabled is changed. How would I go about doing that?

#2

You can create a bindable event and a setter to achieve this.

When you set the variable, you can fire the bindable event!

#3

what is a “setter” in this context

#4

Use Instance:GetPropertyChangedSignal(string: property) or Instance.Changed

Edit: just realized what you wanted. Use the __newindex on a metatable. Ex:

Metatable = {}
Metatable.__newindex = function(selfTable,key,value)
    if key == "Enabled" then
        rawset(selfTable,"Enabled",value)
        -- do stuff with the value variable
        print("set to " .. tostring(value))
   end
end

setmetatable({},Metatable).Enabled = false -- "set to false"
#5

You can create one along the lines of Gun:SetEnabled(bool)

#6

That is just a proxy at that point. The whole point is to detect changes to the property

1 Like
#7 
local Gun = {}
Gun.__index = function(_,key)
    if key == "Enabled" then
        --thing
    end
    return Gun[key]
end

function Gun.new(gunInstance, owner, enabled)
	local metaData = {}
	setmetatable(metaData, Gun)
	
	metaData.Model = gunInstance
	metaData.Owner = owner
	metaData.Enabled = enabled
	
	return metaData
end

return Gun

Perhaps something like this would work for you?

1 Like
#8

Who is listening to the change? If it’s a client then fire the client, which I’m assuming will be found through the Owner data. If it’s the server, then a BindableEvent would be useful. Just remember that only one subscriber can be listening at a time with the Bindable Event.

#9

I am getting some weird stack overflow errors. This is what I tried to do

local Gun = {}
Gun.__index = Gun
Gun.__newindex = function(metaData,key,value)
	if key == "Enabled" then
		metaData.Enabled = value
		print("test", metaData.Enabled)
		-- do stuff with the value variable
	end
end

function Gun.new(gunInstance, owner, enabled)
	local metaData = setmetatable({}, Gun)
	
	metaData.Model = gunInstance
	metaData.Owner = owner
	metaData.Enabled = enabled
	
	return metaData
end

return Gun
#10

You have to index the class table or itll call __index inside __index infinitely

#11

Fixed it, whoops

Forgot to use rawset

#12

How does the code work and why do you need to use rawset

#13

rawset is needed as if I didn’t use it, it would constantly set the Enabled variable again, making an infinite loop. Though now that I think about it, a side effect of this would be that it wouldn’t work again if you set it again so maybe you should have a separate table for the actual values.

#14

Your code doesnt work, even using rawset

#15

Are you running it directly in the command bar?

#16

No, I am running it on the server

local Gun = {}
Gun.__index = Gun
Gun.__newindex = function(metaData,key,value)
	if key == "Enabled" then
		rawset(metaData,"Enabled",value)
		print("test", metaData.Enabled)
		-- do stuff with the value variable
	end
end

function Gun.new(gunInstance, owner, enabled)
	local metaData = setmetatable({}, Gun)
	
	metaData.Model = gunInstance
	metaData.Owner = owner
	metaData.Enabled = enabled
	
	return metaData
end

return Gun
#17 
local Gun = {}
Gun.__index = Gun
Gun.__newindex = function(metaData,key,value)
	if key == "Enabled" then
		rawset(metaData,"Enabled",value)
		print("test", value)
		-- do stuff with the value variable
	end
end

function Gun.new(gunInstance, owner, enabled)
	local metaData = setmetatable({}, Gun)
	
	metaData.Model = gunInstance
	metaData.Owner = owner
	metaData.Enabled = enabled
	
	return metaData
end

return Gun

Try this maybe? Though you should have a separate table for the actual values so that it works a second time due to how newindex works

#18

Why don’t you just put the event inside the constructor function?:

local Gun = {}
Gun.__index = Gun

function Gun.new(gunInstance, owner, enabled)
	local metaData = {}
	setmetatable(metaData, Gun)
	
	metaData.Model = gunInstance
	metaData.Owner = owner
	metaData.Enabled = enabled
	
    gunInstance:GetPropertyChangedSignal("Enabled"):Connect(function()
        -- run code here
    end

	return metaData
end

return Gun
#19

because the enabled shown in the oop function isnt the enabled function in the gunInstance

#20

Anything in “metaData” is the gun instance forever and always because tables are objects