How to refer to a table inside another table?

[szmol96]

Hi. I have this table, where I store my map segments and their data:

Code: Select all

map = {
	a1 = {
		x = 0,
		y = 0,
		width = 640,
		height = 480,
		image = love.graphics.newImage("img/mapa1.png"),
		data = love.image.newImageData("img/mapa1.png")
	},
	a2 = {
		x = a1.x + a1.width, --this is line 11
		y = a1.y,
		width = 640,
		height = 480,
		image = love.graphics.newImage("img/mapa2.png"),
		data = love.image.newImageData("img/mapa2.png")
	},
	b1 = {
		x = a1.x,
		y = a1.y + a1.height,
		width = 640,
		height = 480,
		image = love.graphics.newImage("img/mapb1.png"),
		data = love.image.newImageData("img/mapb1.png")
	},
	b2 = {
		x = a1.x + a1.width,
		y = a1.y + a1.height,
		width = 640,
		height = 480,
		image = love.graphics.newImage("img/mapb2.png"),
		data = love.image.newImageData("img/mapb2.png")
	}
}

But i get this error: "map.lua:11:attempt to index global 'a1' (a nil value)".
If I put "map" there, like this:

Code: Select all

x = map.a1.x + a1.width,

I get another error, which says: "map.lua:11:attempt to index global 'map' (a nil value)"
So, how do I refer to 'a1'?

[Robin]

Well, you can't refer to a table when it doesn't exist yet, so the solution is this:

Code: Select all

map = {
	a1 = {
		x = 0,
		y = 0,
		width = 640,
		height = 480,
		image = love.graphics.newImage("img/mapa1.png"),
		data = love.image.newImageData("img/mapa1.png")
	},
	a2 = {
		width = 640,
		height = 480,
		image = love.graphics.newImage("img/mapa2.png"),
		data = love.image.newImageData("img/mapa2.png")
	},
	b1 = {
		width = 640,
		height = 480,
		image = love.graphics.newImage("img/mapb1.png"),
		data = love.image.newImageData("img/mapb1.png")
	},
	b2 = {
		width = 640,
		height = 480,
		image = love.graphics.newImage("img/mapb2.png"),
		data = love.image.newImageData("img/mapb2.png")
	}
}
map.a2.x = map.a1.x + map.a1.width
map.a2.y = map.a1.y
map.b1.x = map.a1.x
map.b1.y = map.a1.y + map.a1.height	
map.b2.x = map.a1.x + map.a1.width
map.b2.y = map.a1.y + map.a1.height

[szmol96]

Oh, thank you Sir!

EDIT: Oh, and also I need some help with this function. The game says "attempt to index local 'image' (a function value)"

Code: Select all

function maskedHLine(x, y, length, image)
	for i = 1, length do
		local r, g, b, a = image:getPixel( x + i, y )
		if a > 0 then
			return true
		end
	end
	return false
end

It is in connection with this piece of code:

Code: Select all

if maskedHLine(player.x - 11, player.y + 16 + player.ySpeed * dt, 22, currMapSegment) == false then
		if player.ySpeed < player.maxFallSpeed then
			player.ySpeed = player.ySpeed + (1000 * dt)
		end
		player.onGround = false
	else
		player.ySpeed = 0
		player.onGround = true
	end

And I get currMapSegment from this function:

Code: Select all

function currMapSegment()
	local currMapSegment
	local i, segment
	for i, segment in ipairs(map) do
		if player.x >= segment.x and player.x <= segment.x + segment.width and player.y >= segment.y and player.y <= segment.y + segment.height then
			currMapSegment = segment
		end
	end
	return currMapSegment
end

How to solve this one?

[Robin]

Like the error says, currMapSegment is a function.

So:

Code: Select all

if not maskedHLine(player.x - 11, player.y + 16 + player.ySpeed * dt, 22, currMapSegment()) then

(Generally, you'd want to use not something instead of something == false. Boolean logic FTW!)

[ejmr]

(Generally, you'd want to use not something instead of something == false. Boolean logic FTW!)

I disagree. Every one of the following results in boolean false:

Code: Select all

print(1 == false)
print(0 == false)
print(true == false)
print(" " == false)
print(not 1)
print(not 0)
print(not true)
print(not " ")

So I do not believe there is an inherent readability difference between ‘==’ and ‘not’.

[Robin]

So I do not believe there is an inherent readability difference between ‘==’ and ‘not’.

Wat. Your conclusion does not follow from your argument, or you missed a step in between.

People using == true and == false are the bane of my existence.

[foo0]

Code: Select all

if stuff == not false then
	print("blood boiling")
end

[Ref]

Code: Select all

happy = true
if happy then print( 'Smile ') end

[Exasperation]

Wait a second... this:

Code: Select all

not nil

returns true while this:

Code: Select all

nil == false

returns false.

So, since the two options behave differently for the same input, shouldn't we use the one that provides the desired behavior in whatever particular situation we're using it?

[szmol96]

I have difficulties again... The same function gives me a nil value error. It says: "attempt to index local 'image' (a nil value)".
What do I do now?