Experimental/ModuleScripts/Computed.lua

local module = {}

local FF_COMPUTED_CONSTRUCTION_CALLBACK = false
local FF_COMPUTED_REFS = {}

local refValuesById = {}

function module.ref(value: any)
    table.insert(refValuesById, { Value = value, OnSet = {} })
    local id = #refValuesById

    local ref = setmetatable({ 
        Id = id, 
        get = function(self)
            if FF_COMPUTED_CONSTRUCTION_CALLBACK then 
                table.insert(FF_COMPUTED_REFS, self.Id) 
            end; 

            return refValuesById[self.Id].Value; 
        end,
        set = function(self, value: any)
            self.Value = value
    
            task.spawn(function()
                local callbacks = refValuesById[self.Id].OnSet
                for _, callback in callbacks do
                    callback(value)
                end
            end)
        end,
    }, {})

    return ref
end

local computedsById = {}

function module.computed(computationCallback: () -> (any))
    FF_COMPUTED_CONSTRUCTION_CALLBACK = true

    table.insert(computedsById, { Value = computationCallback(), Callack = computationCallback, Refs = FF_COMPUTED_REFS, OnChange = {} })

    local notifyChange = function(refId, compId)
        return function()
            local computedData: { Value: any, Callack: () -> any, OnChange: {  } } = computedsById[refId]
            local newComputedValue = computedData.Callack()
            computedsById[compId].Value = newComputedValue

            for _, callback in computedData.OnChange do
                callback(newComputedValue)
            end
        end
    end

    local refs = FF_COMPUTED_REFS
    if refs[1] then
        for _, ref in refs do
            table.insert(refValuesById[ref].OnSet, notifyChange(ref, #computedsById))
        end
    end

    FF_COMPUTED_CONSTRUCTION_CALLBACK = false
    FF_COMPUTED_REFS = {}

    return setmetatable({ Value = computationCallback(), }, { Id = #computedsById, __index = function(self, key)
        if key:upper() == "VALUE" then
            return computedsById[#computedsById].Value
        else
            return rawget(self, key)
        end
    end})
end

function module.listenEvent(computed: typeof(setmetatable({ Id = 1}, {})), callback: (newValue: any) -> ())
    table.insert(computedsById[computed.Id].OnChange, callback)
end


local Computed = module.computed
local Ref = module.ref
local ListenTo = module.listenEvent




local a = Ref(1)
local b = Ref(2)

local aAndB = Computed(function()
    return a:get() * b:get()
end)

print(aAndB.Value) -- 2

ListenTo(aAndB, print)

a:set(2) 

-- aAndB = 4

b:set(3) 

-- aAndB = 6

return module