Sharing values between metatables

Help and Feedback Scripting Support
1

Hi

I’ve made a post about this before but I think it’s easier to make a new one to not confuse things further.

I have two metatables, for simplicity we’ll call them A and B. There are variables in A which I want to use in B. How would I get said variables from A into B so that they update every single frame (using RenderStepped, preferably). I am aware of rawget/rawset but I dont know if that works every frame - please clarify!

To complicate the matter, B must be required from A to hopefully avoid repeat scripts - I plan to add more metatables which need values from A (I would just require A in B and then pull variables out that way, but I can’t sadly because of cyclic dependency)

Thanks

1 Like
2

I believe it would be simpler to do something like:

local a = {
    x = 0,
    y = 0,
}
local b = {
    z = 0
}
setmetatable(b, {
    __index = a
})
print(b.x) --// prints 0

Make two separate tables A and B, then connect them using a metatable whose __index metamethod is just the table A. B would be able to index values inside A, but A would not be able to index values inside B. When a value in A is updated, it should be updated in B as well via the created metatable.

3

That would work in some situations, but once again the problem of cyclic dependency…

These two metatables are in separate modulescripts (for organization purposes). A is the “instigator” - it requires B so that B can run in the first place. B needs to get values from A, but can’t set A as it’s __index since it can’t require A or the two modules would require each other, i.e. cyclic dependency which luau hates.

It might be possible to have B set A as it’s __index in the ModuleScript for A while all of the code for B runs in the ModuleScript for B. I don’t know.

4

Then just remove the cyclic dependency. There should be a way to do the same thing without having to require A on module B or B on module A. In general, cyclic dependencies are bad in OOP and should be avoided.

5

Not sure if this is what your looking for, but it could be done like this?

-- Module A
local A = {}
A.__index = A

-- Constructor
function A.new(modules: Table)
   local self = setmetatable({}, A)
   self._Modules = modules
   self.Name = "Module A"
   return self
end

function A:HelloFromB()
   print("B said Hello")
end

return A

-- Module B
local B = {}
B.__index = B

-- Constructor
function B.new(modules: Table)
   local self = setmetatable({}, B)
   self._Modules = modules
   self._Modules["A"]:HelloFromB()
   print(self._Modules["A"].Name) -- Should print "Module A"
   return self
end

return B

Now that you have the modules script you would have one main script like so:

-- Main script

local Modules = {}
for _, module in pairs(Modules.Location:GetChildren()) do
   if module and module:IsA("Module") and not Modules[module.Name] then
      Modules[module.Name] = require(module).new(Modules)
   end
end

Of course, you could make your own module system similar to the main script but add more methods such as :GetModule(), and what that would do is return the module from the modules table. Of course, since this isn’t needed but can be done to keep things clean, Hope this helps!

6

If you set __index to a function, you can use rawget(tbl, key) on the other metatable to avoid cyclicity. that’s a fun word

7

Would a third ModuleScript that requires both ModuleScripts suffice?

8

Yes I will probably have to do that, unfortunately. I didn’t want to for organization reasons, but that seems to be the only solution.