Lua OOP: Problems with tables - oop

Question

There some problems with my OOP.
I have parent with clear table and child with same table.
When i'm trying to add object to table of child, object adds to parent's table.
Simple example:
Account = {}
Account.__index = Account
Account.kit = {}
function Account.create(balance)
local acnt = {} -- our new object
setmetatable(acnt,Account) -- make Account handle lookup
acnt.balance = balance -- initialize our object
return acnt
end
function Account:withdraw(amount)
self.balance = self.balance - amount
end
-- create and use an Account
acc = Account.create(1000)
acc:withdraw(100)
table.insert(acc.kit, "1")
print(#Account.kit)
print(#acc.kit)
Result is 1 and 1.
But must be 0 and 1.
How i can isolate child table from parent?

Answer 1

In Lua using acc.kit where acc is a table with the metatable Account will first search the key kit from the table acc and then from table Account.
In your code acc does not have anything with key kit, so the Account.kit will be accessed.
You can solve this simply by defining the kit table for the acc on creation
Account = {}
Account.__index = Account
Account.kit = {} -- You can now remove this if you do not use it - I preserved it to make the test prints to still work.
function Account.create(balance)
local acnt = {} -- our new object
setmetatable(acnt,Account) -- make Account handle lookup
acnt.balance = balance -- initialize our object
acnt.kit = {} -- define kit to be a subtable
return acnt
end
Example:
https://repl.it/B6P1

Answer 2

I'd recommend using closures to implement OOP:
local Animal = {}
function Animal.new(name)
local self = {}
self.name = name
function self.PrintName()
print("My name is " .. self.name)
end
return self
end
--now a class dog that will inherit from animal
local Dog = {}
function Dog.new(name)
-- to inherit from Animal, we create an instance of it
local self = Animal.new(name)
function self.Bark()
print(self.name .. " barked!")
end
return self
end
local fred = Dog.new("Fred")
fred.Bark()
fred.PrintName()
output:
Fred barked!
My name is Fred