Defining Functions by String

[Helvecta]

Hey again! Sorry for all the questions, but I don't even know how I would search for this issue.

And I hardly even know how to describe the issue! Can anybody tell me why the following code fails and a solution to this?

Code: Select all

menu = {}
test = 0

function love.update(dt)
	_G["menu:Open"]()		-- Made of pure evil.
	--menu:Open()			-- Works just fine!
end

function menu:Open()
	test = 1
end

function love.draw()
	love.graphics.print(test, 0, 0)	-- If I *were* able to get to the function, this
	-- would read "1".
end

EDIT: Because it might help,

main.lua:5: attempt to call field 'menu:Open' (a nil value)

[paritybit]

When Lua reads your file, it reads from start to finish in order. When you are calling menu:Open (commented out) in your love.update function, it hasn't yet read the function menu:Open. There are two ways around this. You can declare the menu:Open variable above love.update, or you can move the entire function above love.update.

When you write this:

Code: Select all

function menu:Open()
  test = 1
end

Lua interprets it this way:

Code: Select all

menu.Open = function(self) 
  test = 1
end

[Helvecta]

B-But moving the function above love.update does nothing! Can you give a layman's example?

(Code now is:)

Code: Select all

menu = {}
test = 0

function love.draw()
	love.graphics.print(test, 0, 0) -- If I *were* able to get to the function, test
	-- would read "1".
end

function menu:Open()
	test = 1
end

function love.update(dt)

	_G["menu:Open"]()		-- Made of pure evil.
	--menu:Open()			-- Works just fine!
end

(To make this post a little more functional, could you also explain the benefit of these types of functions? They just seem better for organizing to me, but surely they have more purpose than that..?)

[dreadkillz]

_G["menu:Open"]() is incorrect syntax. You want to do this: _G["menu"]:Open() . I'm not sure why you want to do this though. You already defined menu as a global variable. What's wrong with using menu:Open()?

[Helvecta]

Ah, thank you! This worked like a charm. Did I mention how much i love this forum?

What's wrong with using menu:Open()?

Big edit: Whoa I'm tired. Lemme try to answer that again. I'm using _G[]() instead of things like menu:Open because menu:Open can be shortened even further. I could use an if then else statement to call it depending on what state it is in:

Code: Select all

if state == "normal" then
normal:draw()
elseif state == "menu" then
menu:draw()
elseif ....

end

but it just occurs to me that I can do "_G[state]:draw()" and just define state as what state the game is in and define a function named "menu:draw()", "normal:draw()" and whatnot. It makes it a little easier on the eyes, but other than that, neither is any better, I don't think.

[bartbes]

For that use I usually do something like:

Code: Select all

state = menu

-- further on
state:draw()

[paritybit]

I guess it was too late and I didn't understand what you were asking and just assumed you wanted to use "menu:Open()" but i t was failing for you. And then I did a really poorly executed test and gave you bad advice.

[Helvecta]

For that use I usually do something like:

Code: Select all

state = menu

-- further on
state:draw()

-- ...... This is even better! Why did I have to complicate things?!

And no big deal, Parity, it was like 4am, after all. Thanks for the assistance either way!

And to the rest of you, too: thanks!