Problem - attempt to concatenate local 'y' (a nil value)

[clepto]

Hello, i am beginner in love so take it easy on me

i have watch goature tutorial until number 12 and i tried to create an entity based on his tutorial...

when i try to run i get

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Error: entities/hero.lua:9: attempt to concatenate local 'y' (a nil value)
stack traceback:
	entities/hero.lua:9: in function 'load'
	entities.lua:30: in function 'Create'
	main.lua:11: in function 'load'
	[string "boot.lua"]:378: in function <[string "boot.lua"]:373>
	[C]: in function 'xpcall'

i attached the .love file

any help-suggestions and anything else is more than welcome

[Qcode]

So from what I can tell, on that line you are trying to print the hero's x and y. You have this.

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 print("x is " .. x .. " and y is " .. y)

Which is a perfectly acceptable line of code. So now lets trace back a bit farther to find where the problem is.
That line of code is found in this function

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function ent:load( x, y )

Which is also a correct line of code. The x and y must be defined in a higher function though. Lets go back one more step. This function is called in line 30 in entities.lua

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ent:load()

Though this would be fine, you can see you're missing out on the x and y on the calling.

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ent:load(x, y)

Is what it needs to be changed to.
If you don't define the x and y higher up, then they don't exist, and therefore cannot be printed.

[clepto]

yes your are right! thanks!

but now i get

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Error: entities/hero.lua:4: attempt to index local 'self' (a number value)
stack traceback:
	entities/hero.lua:4: in function 'setPos'
	entities/hero.lua:10: in function 'load'
	entities.lua:30: in function 'Create'
	main.lua:11: in function 'load'
	[string "boot.lua"]:378: in function <[string "boot.lua"]:373>
	[C]: in function 'xpcall'

why?

edit: is there a diffirence in using . or : ? no right?

[Nixola]

There is. Writing ent:load(x, y) is the same as writing ent.load(ent, x, y) but not as writing ent.load(x, y)

[Petunien]

Lua supports a little bit OOP.
The keyword "self" is for objects of a class. But ignore that until you got better and have some experience.

If you are interested in it: http://lua-users.org/wiki/ObjectOrientationTutorial

[clepto]

so whats the right one? the "." ?

@petunien, so i just delete self.? how to solve the problem?

[Petunien]

Both, the "." and the ":" have specific jobs. The ":" is in my opinion useful for objects.

Regarding the error, no, don't just delete it. It won't work then.

I had a look in the code, but actually, I don't understand much.

Please wait until a more experienced user is gonna help you.

[clepto]

Thanks!

lets get back to your problem

[Santos]

Try changing line 10 of hero.lua to:

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self:setPos( x, y )

Using a . instead of a : on this line meant that ent:setPos was receiving only two numbers, instead of the entity itself and two numbers. So the self variable was actually set to the number that x is, hence "attempt to index local 'self' (a number value)". This... is a confusing explanation.

*Finding something from a previous thread!*

function t:f(x, y)

is simply the same as

function t.f(self, x, y)

(They both have the parameter "self". Using the ":", it is hidden!)

and

t:f(x, y)

is simply the same as

t.f(t, x, y)

(Using the ":", the table sends itself as the first parameter.)

If this is still confusing, don't worry. Just call things function which look like function e.f() with e.f(), and functions which look like function e:f() with e:f().

Hope this helps!

[clepto]

thanks! i change the line to

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ent:setPos( x, y )

(also change the self. with ent.) and it running but i cant see anywhere my hero entity...

i have study to do