Function with a script called from another function

Questions
1

Hello,

I have a collection (main) with three objects childs (camera, curseur & galaxy :

  • collection
    ** Camera
    ** Curseur
    ** Galaxy

Curseur and Galaxy have each a script.
In Galaxy script, I put a function (screen_to_world(x, y, z)). Yes, the One And Only.

In Curseur script, I’m calling it.
It’s working :

local action_x, action_y = screen_to_world(action.x, action.y, 9)

put in Curseur.script, and screen_to_world() put in Galaxy script, still give me flawlessly the good result.

I don’t understand : Shouldn’t it fail ?
I don’t complain, but I thought function were local to the script where they are ?

2

Functions are only local if you add the local keyword in front of them. Did you do that with screen_to_world()?

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3

No. I didn’t.
Function and Variable are the same thing, then ? Same scope rules ?

4

They are the same thing. These two are equivalent:

function foobar()
   print("Hello")
end

foobar = function()
   print("Hello")
end

Functions are values and they can be assigned to variables. In the above example there’s a variable named foobar and the value assigned to the variable is a function which prints “Hello”.

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5

But how can I make sure a function can’t be called by another script ?

7

Put local in front of it:

local function foobar()
  print("Can't be called by another script")
end
8

Already tried that, but I have an error message as answer :

ERROR:SCRIPT: main/Curseur/Curseur.script:128: attempt to call global ‘Wheel_Zoom’ (a nil value)

The line 128 :

Wheel_Zoom(1, self)

The function (out of the lifecycle, in last position in the script) :

local function Wheel_Zoom(sens, self)

		self.wheel = 0
end

Works flawlessly without the “local”, though.

9

Make sure you’re defining the local function before calling it, since the function doesn’t get hoisted.

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10

The reference to anything you create gets stored in the global Lua table, by default. This means it can be accessed directly, from anywhere. This is really really not a good idea. Always use the local keyword. If you want to use the same function in more than one place, define it in a Lua module. The more you limit scope the better; Lua is great for doing this.

2 Likes
11

I put the function Wheel_Zoom before all the others (but Init, because you never know), and it’s working with in Local now.

It’s weird, I though the engine would parse the code before executing it.

Thank you for your answers.

12

I haven’t worked with Lua before Defold, so I’m not an authority on the subject, but I believe this doesn’t have anything to do with the engine and is just a property of Lua the language:

Functions are just variables. You can’t access a variable before you define it, right?

print(name) -- this would just print "nil" since the variable hasn't been defined
local name = "Hunter"

I also don’t believe there’s anything special about init - it’s just a lifecycle hook, a function that is called at some point in the game object’s lifecycle like all the others.

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