need a bit of help with OOP in LUA

[blenderer]

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        --OOP Sandbox

	player = {name, level, class}
	function player:new()
		setmetatable(self)
		self.__index = self
	end
	
	testplayer = player:new()
	testplayer.name = "testplayer" --errors are coming from these lines
	testplayer.level = 80                -- here
	testplayer.class = "Warrior"     --and here

Okay, I have been trying to learn and research how to do basic classes and Object Oriented Programming with LUA, but the guides/references on the web are a bit confusing. I understand why LUA is different than other languages but I am having trouble figuring out syntax and other stuff.

All I want to do is create a basic class and create objects out of it.
I want to reference stuff like:

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print testplayer.name

but I am getting an error in the first code block saying

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attempt to index global 'testplayer' (a nil value)

Thanks so much in advance!!

[Simtex]

Since I don't know how familiar you are with Lua in general, my explanation may be hard to understand.

First of all the specific problem you are having is because of this line:

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   testplayer = player:new()

In Lua terms, this line first runs the player:new() function, takes whatever value that function returns, and makes testplayer equal to it. Since player:new() doesn't return any value, testplayer is made equal to nil, which is equivalent to never initializing testplayer at all.

The other problem you are having is that you are not creating new objects from your class. In your current code you are attempting to essentially make testplayer equal the "player" class. Instead, you need to create a new object from the blueprint that is the "player" class. I apologize if that was hard to understand.

The quick fix for your problem is as follows:

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   player = {name, level, class}

   function player:new()

      local obj = {} --First line to add, this creates a new table called obj.  Check the Lua documentation if you don't know what "local" means here.

      setmetatable(obj, self) --Line change here, this sets the metatable of your new object to the classes metatable, this is essentially what makes "obj" an object created from the class "player"

      self.__index = self

      return obj  --Second line to add, this returns the new object you just created from your class.

   end

Here's the new code in total without my comments:

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        --OOP Sandbox

   player = {name, level, class}
   function player:new()
      local obj = {}
      setmetatable(obj, self)
      self.__index = self
      return obj
   end
   
   testplayer = player:new()
   testplayer.name = "testplayer" --errors are coming from these lines
   testplayer.level = 80                -- here
   testplayer.class = "Warrior"     --and here

If you'd like, you can add this to the end so you can see what testplayer is initialized to when you run that code in LOVE:

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function love.draw()

	love.graphics.print("testplayer.name = " .. testplayer.name, 50, 50)
	love.graphics.print("testplayer.level = " .. testplayer.level, 50, 75)
	love.graphics.print("testplayer.class = " .. testplayer.class, 50, 100)

end

[kikito]

Shameful plug here: You may want to have a look at MiddleClass. You can use it directly and "forget" about the metatables, or have a look at its code and see how things work internally.

But yes, the problem you were having is that for making OOP you need to star creating a table that represents the "class". This class, in turn should have a "new" method that creates other tables (the "instances").