Proxy Tables

by:

haotian2006

Pre-requisites

Before reading this tutorial, you should know about metatables. An explanation of metatable exists in the Lua-Learning folder (not anymore).

What are Proxy Tables?

proxy table are Tables that allow you to detect when a table is updated or changed using __newindex

function Proxy:GetValue(key)
    return self.RealData[key]
end
function Proxy:SetValue(key,value)
    self.RealData[key] = value
    print("Detected Change at",key,"new Value",value)
end

How to set on up

what we want to do it use __newindex to reference the Real Data inside of the Proxy Table.

We can set it up like this:

local Proxy = {}

Proxy.__newindex = function(self,key,value)
    self.RealData[key] = value -- without this the key would need be set to the new value
    print("Detected Change at",key,"new Value",value)
end


function Proxy.new(DataTable)
    return setmetatable({RealData = DataTable or {}},Proxy)
end

return Proxy

This is basically all you need for a proxy table to function

local Proxy = require(Path.To.Proxy.Module)
local data ={
    A = 1,
    Hao = 2
}
local ProxyTable = Proxy.new(data)

ProxyTable.A = 2 --> Detected Change at A new Value 2
ProxyTable.B = 3 --> Detected Change at B new Value 3
ProxyTable.Hao = nil --> Detected Change at Hao new Value nil

Features you can add to your proxy table

you can also add more features to the proxy table so that the proxy table can act like a normal table. here are some examples:

adding the __index metamethod

-- this will allow you to do ProxyTable["A"] normally to get the data
Proxy.__index = function(self,key)
    return self.RealData[key]
end

--Example Use Case
print(ProxyTable.ProxyTable.A) -- > 2
print(ProxyTable.A) -- > 2

adding the __iter metamethod

-- this will allow the proxy table to be iterated by a for loop
Proxy.__iter = function(self)
    return next,self.RealData -- similar to pairs(table)
end

--Example Use Case
for i,v in ProxyTable do
    print(i,v) --> A 2 | B 3
end

adding a bindable event to use as a changed event

-- this will allow the proxy table to be iterated by a for loop
Proxy.__newindex = function(self,key,value)
    self.RealData[key] = value
    self.Changed:Fire(key,value)
end

function Proxy.new(DataTable)
    return setmetatable({RealData = DataTable or {},Changed = Instance.new("BindableEvent")},Proxy)
end

--Example Use Case
ProxyTable.Changed.event:Connect(function(key,value)
    print("table was modified")
end)

Check out this link for more metamethods

Conclusion

if you think you’re going to use RealData as a key name you can name the key to something random so that when you do ProxyTable.RealData= it wouldn’t override your real data with an empty table. Anyways thats it for this tutorial, hope this helps