"Attempt to get length of nil value"?

[NolanCYT (Him)]

I’m making a Roguelike game and I am currently working on the Dungeon Generation using an open source Dungeon Generation page I found on GitHub. So far it’s working fine, but I’ve encountered an error that seems very simple, I just don’t know how to go about fixing it. Here’s a screenshot:

Here is the function that is causing the error:

function Level:getRoomTree()
	if #self.rooms < 1 then error("Can't generate room tree, no rooms exists") end
	
	local root, lastLeaf = prims(table.clone(self.rooms)) -- This is the line causing the error
	self.rootRoom = root
	self.endRoom = lastLeaf

	return root
end

I decided I’d print out the value that the prims function is receiving and it returned nil,

Here is the code for the prims function:

function HelpFunctions:prims(unvisited)
	print(unvisited)
	local len = #unvisited
	local root = remove(unvisited, 1)
	if #unvisited==0 then return root, root end

	local visited={}
	insert(visited, root)
	local v0
	local endIndex
	repeat
		local dist = 1e309    -- ~inf
		for i = 1, #visited do
			for j = 1, #unvisited do
				if (unvisited[j]:distanceTo(visited[i]) < dist) then
					dist = unvisited[j]:distanceTo(visited[i])
					v0 = visited[i]
					endIndex = j
				end
			end
		end
		local v1 = remove(unvisited, endIndex)
		v0:addNeighbour(v1)
		insert(visited, v1)
	until #visited == len

	return visited[1], visited[#visited]
end

I’m just a bit confused, help is appreciated! Thanks!

[Darkmist101 (Darkmist)]

Directly use HelpFunctions:prims, making a variable pointing to it’s function changes the meaning.

function HelpFunctions:prims(unvisited) --> HelpFunctions.prims(self, unvisited)

The self is implicit, the calling object. So you’d have to do prims(HelpFunctions, unvisited), but why would you do that in this case?

[NolanCYT (Him)]

This actually worked perfectly! Thank you so much!

[Darkmist101 (Darkmist)]

To note, you could look at all of the helper functions, and look if the keyword self is used, if it’s not you can change all the function definitions to be HelperFunctions.func_name, and store references as you wish. I’d actually assume by it’s name it’s containing pure functions, that you should be able to do that; but going and editing the modules like that sort of defeats the off-the-shelf nature of it.