How to make an objects variables private?

Hey, I'm trying my hand at Object Oriented programming. Compared to java, I'm really having a hard time making the members of an object private, and some functions public.

Here is my code. It is in a ModuleScript

local Pizza = {}

function Pizza.new(...)
	return setmetatable({
		Slices = 8;
		Toppings = {...};
		Cooked = false;
	}, Pizza)
end

Pizza.__index = Pizza

function Pizza:eat(x)
	if x ~= nil then
		self.Slices = self.Slices - x;
	else
		self.Slices = self.Slices - 1;
	end
end

function Pizza:addTopping(x)
	table.insert(self.Toppings, x);
end

Pizza.__newindex = function()
	error("Pizza object is private");
end



return Pizza

And this is what I use to test it

pepperoni = Pizza.new("Pepperoni");
print(pepperoni.Slices);
pepperoni.Slices = 2;
print(pepperoni.Slices);
pepperoni.cheese = 5;

Problem is, setting pepperoni.Slices will indeed change the value of Pepperoni.Slices. How in the world do I make the variable Slices private, so it can't be changed, and my data is protected?

'local' is the same thing as making a private value in Java.

So

local cake = 10
do
	print(cake)
end

Output:

nil

In Lua values are local to the scope of code that they're in. So creating a value outside of a scope will make it not exist in said scope. If you don't put "local" behind the value name then it is a public value.

In your case, your code should look like this:

do

local Pizza = {}

	function Pizza.new(...)
   	 return setmetatable({
     	   Slices = 8;
    	    Toppings = {...};
   	     Cooked = false;
  	  }, Pizza)
	end

	Pizza.__index = Pizza

	function Pizza:eat(x)
  	  if x ~= nil then
  	      self.Slices = self.Slices - x;
  	  else
    	    self.Slices = self.Slices - 1;
 	   end
	end

	function Pizza:addTopping(x)
	    table.insert(self.Toppings, x);
	end

	Pizza.__newindex = function()
 	   error("Pizza object is private");
	end



	return Pizza

end

----

--This is outside of the scope, it will return a error.
pepperoni = Pizza.new("Pepperoni");
print(pepperoni.Slices);
pepperoni.Slices = 2;
print(pepperoni.Slices);
pepperoni.cheese = 5;

Though your problem is irrelevant: if you want your data to be protected just turn on FilteringEnabled.