Function Parameters in LUA

General
1

This seems like such an elementary question, but I seem to be missing something. I have an object with a function. I pass it two parameters, and the first one is always tossed. This only occurs on non-constructor functions.

For example:

Main.file
...
ballA = Ball(x,y,w,h)
ballA.printOut(10,20)
...

~

Ball.file
...
function Ball:printOut(a,b)
print("a", a, "b", b)
end
...

~
Output:
a 20 b nil

Something similar happens when I pass a vec2 as a parameter too. I only get the y value of the vector.

2

Have you created the Ball class? Look at this code below, which works fine, and see if you can find what you are missing.

function setup()
    myRobot = Robot()
    myRobot:speak("Hello","There")
    myRobot:move(vec2(50,200))
end

function draw()
    background(0, 0, 0, 255)
end

--You can put the class code below in a separate file if you like

Robot = class()

function Robot:init()
    print "new robot created."
end

function Robot:speak(firstword,secondword)
    print("1:",firstword,"2:",secondword)
end

function Robot:move(newLocation)
    print ("Moved. New location is " .. newLocation.x .. ", " .. newLocation.y)
end
3

I believe function Ball:printOut(a, b) (with a colon) is shorthand for

Ball["printOut"] = function (self, a, b) ... end

By using a dot rather than the colon, you are calling the function with only self set to 10 and a set to 20 (and b set as nil).

4

I found that the error was caused by creating my function with a “:” instead of a “.”.

Found that info here http://www.lua.org/pil/16.html

Still don’t really understand it though.

5

Oh, I didn’t refresh. Thanks for the pointers guys.

6

Actually, you should create the function with a colon : and then call it with a colon as well. You call it with BallA.printOut(10,20) but it should be BallA:printOut(10,20)