ERROR: "attempt to index global 'self' (a nil value) - lua

Question

I'm very slowly working my way through the games track of cs50, and I am stuck on Mario3. In the video he just talks about the code, but I wanted to write it into my own that I am writing alongside the video. I have the exact same code that he does, but I keep getting this error and I cannot figure out why. I will post the code below, but as far as I can tell, I have already assigned self.mapWidth = 30, so I don't know why it keeps saying that it is a nil value.
Here is the error
Error code
Here is the map.lua code
require 'Util'
Map = Class{}
TILE_BRICK = 1
TILE_EMPTY = 4
--cloud tiles
CLOUD_LEFT = 6
CLOUD_RIGHT = 7
SCROLL_SPEED = 62
function Map:init()
self.spritesheet = love.graphics.newImage('graphics/spritesheet.png')
self.tileWidth = 16
self.tileHeight = 16
self.mapWidth = 30
self.mapHeight = 28
self.tiles = {}
self.camX = 0
self.camY = 0
self.mapWidthPixels = self.mapWidth * self.tileWidth
self.mapHeightPixels = self.mapHeight * self.tileHeight
self.tileSprites = generateQuads(self.spritesheet, self.tileWidth, self.tileHeight)
--fill map with empty tiles--
for y = 1, self.mapHeight do
for x = 1, self.mapWidth do
self:setTile(x, y, TILE_EMPTY)
end
end
for y =self.mapHeight / 2, self.mapHeight do
for x = 1, self.mapWidth do
self:setTile(x, y, TILE_BRICK)
end
end
end
function Map:setTile(x, y, tile)
self.tiles[(y - 1) * self.mapWidth + x] = tile
end
function Map:getTile(x, y)
return self.tiles[(y -1) * self.mapWidth + x]
end
local x = 1
while x < self.mapWidth do
if math.random(20) == 1 then
local cloudStart = math.random(self.mapHeight / 2 -6)
self.setTile(x, cloudStart, CLOUD_LEFT)
self:setTile(x + 1, cloudStart, CLOUD_RIGHT)
end
end
function Map:update(dt)
if love.keyboard.isDown('w') then
self.camY = math.max(0, math.floor(self.camY - SCROLL_SPEED * dt))
elseif love.keyboard.isDown('s') then
self.camY = math.min(self.mapHeightPixels - VIRTUAL_HEIGHT, math.floor(self.camY + SCROLL_SPEED * dt))
elseif love.keyboard.isDown('a') then
self.camX = math.max(0, math.floor(self.camX - SCROLL_SPEED *dt))
elseif love.keyboard.isDown('d') then
self.camX = math.min(self.mapWidthPixels - VIRTUAL_WIDTH, math.floor(self.camX + SCROLL_SPEED * dt))
end
end
function Map:render()
for y = 1, self.mapHeight do
for x = 1, self.mapWidth do
love.graphics.draw(self.spritesheet, self.tileSprites[self:getTile(x, y)],
(x - 1) * self.tileWidth, (y - 1) * self.tileHeight)
end
end
end
and in case you need it, here is my main.lua code
WINDOW_WIDTH = 1200
WINDOW_HEIGHT = 720
VIRTUAL_WIDTH = 432
VIRTUAL_HEIGHT = 243
Class = require 'class'
push = require 'push'
require 'Util'
require 'Map'
function love.load()
map = Map()
love.graphics.setDefaultFilter('nearest', 'nearest')
push:setupScreen(VIRTUAL_WIDTH,VIRTUAL_HEIGHT,WINDOW_WIDTH,WINDOW_HEIGHT, {
fullscreen = false,
resizable = false,
vsync = true
})
end
function love.update(dt)
map:update(dt)
if love.keyboard.isDown('escape') then
love.event.quit()
end
end
function love.draw()
push:apply('start')
love.graphics.translate(math.floor(-map.camX),math.floor(-map.camY))
love.graphics.clear(108/255, 140/255, 1, 1)
map:render()
push:apply('end')
end
Thanks in advance for any and all help.

Answer 1

function Map:SomeFunction() end is syntactic sugar for Map["SomeFunction"] = function(self) end
Therefor you can use self inside a function defined with the colon syntax.
Outside of such a function self is nil.
Yet you index self several times in this while loop where self is nil.
local x = 1
while x < self.mapWidth do
if math.random(20) == 1 then
local cloudStart = math.random(self.mapHeight / 2 -6)
self.setTile(x, cloudStart, CLOUD_LEFT)
self:setTile(x + 1, cloudStart, CLOUD_RIGHT)
end
end
which is an infinite loop btw.