Small LUA question

[zd]

This isn't specific to LOVE, but I'm having trouble finding an answer elsewhere so I figured I'd give it a shot here.

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function countWalls(tiles)

	local walls = 0

	for x = self.x - 1, self.x + 1 do
		for y = self.y - 1, self.y + 1 do
			if tiles[x][y] == nil then -- doesn't work, but needs to
				walls = walls + 1
			elseif tiles[x][y].blocked == true then
				walls = walls + 1
			end
		end
	end

	return walls

end

My question is how exactly should

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if tiles[x][y] == nil then -- doesn't work, but needs to

Is there a handy and quick way to check whether or not a given variable exists?

I just keep getting

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line 28: attempt to index field '?' ( a nil value )

Now, I've actually been able to rectify this pretty easily by adding code to the function to ignore border tiles. That being said, I would really like to know of an elegant way to check whether or not a variable might exist without it throwing an error when it doesn't. I'll post up a sample of my game once I get this refactor done.

[veethree]

What's on line 28?

It'd help if you'd post the whole .love, That makes it easier for us to troubleshoot.

[Kadoba]

You've got the right idea. The problem is that something in the first dimension of your 2d array is nil. To prevent this from causing an error you need to change your code here:

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if tiles[x][y] == nil then 

to this:

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if tiles[x] == nil or tiles[x][y] == nil then

Another trick is that nil is the only thing besides false that does not resolve to true in logical expressions, so you can do this as a shortcut:

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if not tiles[x] or not tiles[x][y] then

I created a grid class to make working with 2d arrays easier. Here it is if you're interested.

[zd]

You've got the right idea. The problem is that something in the first dimension of your 2d array is nil. To prevent this from causing an error you need to change your code here:

Code: Select all

if tiles[x][y] == nil then 

to this:

Code: Select all

if tiles[x] == nil or tiles[x][y] == nil then

Another trick is that nil is the only thing besides false that does not resolve to true in logical expressions, so you can do this as a shortcut:

Code: Select all

if not tiles[x] or not tiles[x][y] then

I created a grid class to make working with 2d arrays easier. Here it is if you're interested.

Thanks man, this worked perfectly.