Making and using an object-style Module in Lua - object

Question

I've been trying to take a module in Lua and use it to imitate an object. i.e. I made a deck of cards:
local Card = require("Card")
local function firstCard()
Card.newDeck()
Card.drawCard()
return Card.getCard()
end
local function secondCard()
Card.newDeck()
Card.drawCard()
return Card.getCard()
end
first = firstCard()
second = secondCard()
print(first)
print(second)
I set first = firstCard() and second = secondCard() but when I print the two variables second occasionally results as nil. I'm honestly lost. Here's the actual module itself.
local Card = {}
local deck
local value
local number, suit
local index = 0
local getCard
local getValue
function Card.newDeck()
deck = {}
value = {}
for x = 1, 13 do
if x == 1 then
number = "Ace"
elseif x == 11 then
number = "Jack"
elseif x == 12 then
number = "Queen"
elseif x == 13 then
number = "King"
else
number = x
end
for x1 = 1, 4 do
if x1 == 1 then
suit = "Clubs"
elseif x1 == 2 then
suit = "Diamonds"
elseif x1 == 3 then
suit = "Hearts"
else
suit = "Spades"
end
index = index + 1
deck[index] = number.." of "..suit
value[index] = x
end
end
end
function Card.drawCard()
index = math.random(52)
getCard = deck[index]
getValue = value[index]
end
function Card.getCard()
return getCard
end
function Card.getValue()
return getValue
end
function Card.getIndex()
return index
end
return Card
I have limited knowledge of Lua when it comes to Object-Oriented programming and to be honest, I typically only use it for calculations or small games to keep me occupied I'm class- I'm only 16. I'm more used to Java, even though I started using Lua well before I picked up Java. I just want to know if and how I can make this work. For the most part it works, just those occasional nil values.

Answer 1

The problem is that you have declared the index variable local at the top level of your module. That means that the random value of index that you have calculated in your first drawCard() is reused in your second call to newDeck(). You can add print(index) at the start of newDeck() to see what I mean.
There are several ways to solve the problem. One would be to add index = 0 at the top of newDeck(). A better one would be to declare your variables with smaller scoping, i.e. make index local to each function that uses it.

Answer 2

Try to use this instead, seems to work fine, it should print "ERROR NO VALUE" if there is some issue with the index, if that occurs (it shouldn't though), just print the index (in the generateCard() function).
This is the test
local Card = require("Card");
local function firstCard()
Card.newDeck()
return Card.generateCard(); -- two parameters, deck and value
end
local function secondCard()
Card.newDeck()
return Card.generateCard();
end
first = firstCard()
second = secondCard()
print(first)
print(second)
This is the module
local Card = {deck={};value={};};
function Card.newDeck()
local self = Card
local deck = self.deck;
local value = self.value;
local cards = {[1]="Ace",[11]="Jack",[12]="Queen",[13]="King"};
local types = {[1]="Clubs",[2]="Diamonds",[3]="Hearts",[4]="Spades"};
for x = 1, 13 do
for i = 1, 4 do
local _card,_type=(cards[x] or x),types[i];
deck[#deck+1] = _card.." of ".._type
value[#deck+1] = x
end
end
end
function Card.generateCard()
local self = Card;
if(not math.round) then
math.round = function(value) local mi,ma=math.floor(value),math.ceil(value)return(mi+0.5>value and mi or ma)end;
end
local index = math.round(math.random(1000, 52000)/1000);
return (self.deck[index] or "NO VALUE FOR CARD"),(self.value[index] or "NO DECK FOR CARD");
end
return Card