Monitor Lua table access and update

monitor_table.lua

-- table to monitor
ori_t = { a = "b" }
    
-- a proxy table - must be empty
proxy_t = {}

local mt
do
   mt = {
      __index = function (self, k)
         print("*access to element " .. tostring(k))
         return ori_t[k]   -- access the original table
      end,

      __newindex = function (self, k, v)
         print("*update of element " .. tostring(k) ..
               " to " .. tostring(v))
         ori_t[k] = v   -- update original table
      end
   }
end

setmetatable(proxy_t, mt)

proxy_t[2] = 'hello'
print(proxy_t[2])

proxy_t["a"] = 'hello'
print(proxy_t["a"])

Refer to https://stackoverflow.com/questions/57598440/is-there-a-way-to-listen-for-changes-in-a-lua-table.