"Variable nil" error

[Refpeuk]

Hey Guys,

I've been staring at my code, running it through over and over, and still can't figure out why it thinks one of my local variables is nil: I assign it a value directly before I use it.

I've included the .love that crashes - the error shows exactly which variable, where, and the chain of functions that ends up calling it. (It's in the character class in the rotate function)

I'd appreciate any help; I don't know if I'm just missing something crazy obvious?

[kraftman]

You can't pass over the return values of functions like that, so as far as character:rotate is concerned it is only receiving wmy and wmy, which are actually the x values of the mouse and character:center functions

[Refpeuk]

Oh, I see. I thought it worked the same was as assigning multiple variables. Eg:

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local wmx,wmy = mouseworld(love.mouse.getPosition())

Thanks for that!

[kraftman]

Oh, I see. I thought it worked the same was as assigning multiple variables. Eg:

Code: Select all

local wmx,wmy = mouseworld(love.mouse.getPosition())

Thanks for that!

no problem, to be honest ive never tried doing something like that so im not sure how it does work. Oh well!

[Refpeuk]

Oh right, I also meant to ask - if it was only recognizing two variables, why did it throw the error at py instead of px, which came first?

[Robin]

So, what is going on here?

As you know, in Lua, functions can return multiple values

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function t1()
   return 1, 2, 3
end

And you can pass them to other functions:

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function t2(a, b, c)
   return a + b + c
end

print(t2(t1())) -- prints 6

However, that only works if no other arguments follow it. So:

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print(t2(t1(), 10, 20)) -- prints 31

Why does it do that?

If other arguments follow the function call, it only uses the first return value:

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print(t2(1, 10, 20))

So in your case, you call

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character:rotate(mouseworld(love.mouse.getPosition()), characterdat[num].shape:center())

which means the arguments to character:rotate() become:

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local wmx = mouseworld(love.mouse.getPosition()) -- only the first return value
local wmy, px = characterdat[num].shape:center()
local py = nil

Does that make it clear?

[Refpeuk]

It does, thanks!