Lua Syntax Error

Questions
1

Hey guys. I spent that last few months in C# and now coming back to Codea, I cant write Lua code to save my life.

It has a problem with self in

for i = 1, #self.ants do

in the draw function.

Edit: fixed the “:” in draw

Game = class()

function Game:init()
    self.ants = {}
    self.numberOfAnts = 5
    self:CreateAnts()
end

function Game:draw()
    print(#self.ants)
    for i = 1, #self.ants do
        self.ants[i]]:draw()
    end
end

Whats the problem here?

2

what does self:createAnts()?

3

Also, shouldn’t it be

self.ants[i]:draw()

? With a “:” rather than a “.”? I know what you mean btw, I’ve been working in Java for a while and coming back to Lua is weird.

4

@se24vad Its a function thats not shown.

@TheSolderKing That was a mistake, but it doesnt explain why it doesnt recongize “local self” in the print statment.

5

When you call the draw function, you are probably doing it with a “.” and not a “:”, eg

g=Game()
g:draw()   <--- use :
6

Yes, if you call a method with dot notation, the method won’t be able to access self, or rather it will look for self in the first argument that is passed to it.

instance:draw(args) is just a shorthand for myClass.draw(instance, args)

7

I’ve always wondered, why does Lua use the “:” rather than the “.”? I presume it is to make a distinction between being able to access self and not being able to, but if that is the case why not make the default “.” like in most other languages?

8

You guys are right, using “.” to call game’s draw was the problem. Thanks.

Can you use the “.” to pass a different self when calling a function of an instance, other than the appropriate one? Why would that be useful?

9

You can pass a different self, though you’re right that you probably wouldn’t want to. What it is very useful for, is for passing self to methods that are outside of the class (I think this is called meta-methods? You could call this a kind of multiple-inheritance ), or, in class-inheritance, invoking a method from the master class that the subclass has overwritten. Eg in mySubclass:init(args) you might call myMasterClass.init(self,args).

10

Self is just a word for the address of the current class instance.

You would pass a different self like this

A=someClass(). --<-- A holds the address of a table
B=someClass(). --<-- so does B
A:hits(B) --<-- this passes both tables to the hits function
A.hits(A,B) --<-- this does exactly the same thing
print(B.eye) --<--- "black"

function someClass:Hits(target)
    self.hand="sore" --<--- self refers to the same table as A
    target.eye="black"
end

PS the reason I knew what the error was, is that I made the same error many times when first learning Codea, so I remember it well :stuck_out_tongue:

11

Cool, I learned something new today. Thanks.

12

You can pass a different self, though you’re right that you probably wouldn’t want to.

But sometimes you want to fool the system and call a method on an instance of another class. This is how inheritance is implemented, for example:

Parent = class()
Child = class(Parent) -- inherit all methods from Parent

function Child:init() -- this overwrites the inherited initialisation function
    Parent.init(self) -- so this is a way of calling the Parent init function on us
    -- do some new stuff
end