stop using module() ok

main.lua

local mod = require "mod"

print(mod.func, mod.x)
-- 100, function: 0xFFFFFFFF

print(mod.priv, priv)
-- nil, nil

mod.lua

local function priv(x)
  return x * 2
end

local mod = {
  x = 100
}

function mod.func(x)
  self.x = x
  return priv(self.x)
end

return mod