self.action button example help please!

General
1

Hi, I’m looking at the button code in the Sounds Plus example in the Codea app.

I am trying to understand what this means:

if self.action then 

    self.action()

end

What is this part doing? I see self.action is set to nil in the init part…so that is nil…but what is self.action()? what do the brackets do after it? anything close to an explanation would help!!!

2

The action which the button performs. The self.action() means the action is changed from nil elsewhere

3

I still don’t understand, sorry. How can a variable (self.action) also be the name of a function (self.action())? is this allowed?

4

Because self.action ( a variable ) is a pointer to a function. It’s originally set to nil in Button:init but later set to point to a function in the other classes. So if it’s not nil, then it’s pointing to a function.

5

Ok, so, self.action starts as nil, then when the button is pressed it changes and runs the function from Main.lua…

Question: If self.action is set to nil at init, why does it still activate the if function? isn’t nil like FALSE?

6

Or in simpler terms

If (the function self.action does not exqual false i.e. exists) then
    run self.action
end
7

Maybe this will help explain what we’re talking about.


function setup()
    func="this is a string"
    print(func)
    print()
    
    func=123456
    print(func)
    print()
    
    func=func1
    print(func)
    func()
    print()
    
    func=func2
    print(func)
    func()    
end

function func1()
    print("executed func1")
end

function func2()
    print("executed func2")
end
8

And nil is blank or empty, not false

9

Thanks guys! I think I understand now. LOVE CODEA!

10

@david19801,
do you have Skype?

11

Just to correct one thing.

if var then
...
end

The condition is false if var is false or nil and true otherwise.