Help wanted initializing a lua table [SOLVED]

Questions
1

Hi all.
I was playing around with an idea ( Codea! :wink: ) of mine using a @dave1707’s fantastic piece of code (a “physics shooter”), trying to shoot two simultaneous bullets at a big target. Everything was fine when I created the bullets one by one “by hand” (the code lines commented out below), but when I wanted to automatize the bullets’ creation with a “for loop”, I got the error message of “trying to index a nil value”. I do know that Lua tables are one the most striking features of the language and any help would be appreciated. Thanks in advance ~O)

displayMode(FULLSCREEN)
function setup()
    m=0
--    b1={}
--    b2={}
    b={}
    lv=vec2(400,0)
    cyl=physics.body(CIRCLE,30)
    cyl.x=WIDTH/2
    cyl.y=HEIGHT/2
    cyl.type=STATIC
    physics.gravity(0,0)
end

function draw()
    local x,y
    background(232, 232, 19, 255)
    fill(255, 23, 0, 255)
    ellipse(cyl.x,cyl.y,cyl.radius*2)
    for z=1,m do
--        x=b1[z].x
--        y=b1[z].y
--        x2=b2[z].x
--        y2=b2[z].y
        fill(0, 74, 255, 255)
        for i=1,2 do
            ellipse(b[i][z].x,b[i][z].y,10)
        end
--        ellipse(x,y,10)
--       ellipse(x2,y2,10)
    end
end

function shoot(x)
--    b1[x] = physics.body(CIRCLE,5)
--    b1[x].x=20
--    b1[x].y=HEIGHT/2-10
--    b1[x].linearVelocity=lv
--    b2[x]=physics.body(CIRCLE,5)
--    b2[x].x=20
--    b2[x].y=HEIGHT/2+10
--    b2[x].linearVelocity=lv
--    b[1]={}
--    b[2]={}
    for i=1,2 do -- I tried this, but failed
        b[i][x]=physics.body(CIRCLE,5)
        b[i][x].x=20
        b[i][x].y=HEIGHT/2-i*10
        b[i][x].linearVelocity=lv
    end
end

function touched(t)
    if t.state == BEGAN then
        if CurrentTouch.x > WIDTH/2 then
            m = m + 1    
            shoot(m)
        end
    end
end
2

You need to insert this line

for i=1,2 do
    b[i]=nil --insert this

because a table can hold anything. If you want it to hold sub tables, then each of them needs to be defined first

If you want to delete bullets later, do it like this

--to delete bullet number 3
b[3][x]:destroy() --gets rid of physics object, must be done first
b[3][x]=nil --deletes table entry
3

Thanks @Ignatz, but it didn’t work. I tried inserting b[i]={} also, but it didn’t work neither.

4

Yes, I should have written {} instead of nil, I wasn’t thinking straight, too early in the morning!

This works for me

function shoot(x)
    for i=1,2 do
        b[i]={}                                           --the extra line
        b[i][x]=physics.body(CIRCLE,5)
        b[i][x].x=20
        b[i][x].y=HEIGHT/2-i*10
        b[i][x].linearVelocity=lv
    end
end
5

Good morning!
Well, sorry, what I want to do is shooting with every screen touch. Inserting the afore mentioned line, it works just for the first shot, but not for the second shot (i.e. touch) and so on.

Edit: well, the error appears now when the draw function is called.

6

@quezadav - Try this

displayMode(FULLSCREEN)
function setup()
    m=0
--    b1={}
--    b2={}
    b={}
    lv=vec2(400,0)
    cyl=physics.body(CIRCLE,30)
    cyl.x=WIDTH/2
    cyl.y=HEIGHT/2
    cyl.type=STATIC
    physics.gravity(0,0)
end

function draw()
    local x,y
    background(232, 232, 19, 255)
    fill(255, 23, 0, 255)
    ellipse(cyl.x,cyl.y,cyl.radius*2)
    for z=1,m do
        fill(0, 74, 255, 255)
        for i=1,2 do
            if b[z][i] then --only continue if this bullet still exists
                --destroy bulet if it goes off screen
                if b[z][i].x<0 or b[z][i].x>WIDTH or b[z][i].y<0 or b[z][i].y>HEIGHT then 
                    b[z][i]:destroy() --destroy physics object
                    b[z][i]=nil --remove item from table
                else ellipse(b[z][i].x,b[z][i].y,10) end
            end
        end
    end
end

function shoot(x)
    b[x]={}
    for i=1,2 do
        b[x][i]=physics.body(CIRCLE,5)
        b[x][i].x=20
        b[x][i].y=HEIGHT/2-i*10
        b[x][i].linearVelocity=lv
    end
end

function touched(t)
    if t.state == BEGAN then
        if CurrentTouch.x > WIDTH/2 then
            m = m + 1    
            shoot(m)
        end
    end
end
7

Hi! It’s morning now in Mexico. :-h
@Ignatz, solved, brilliant! =D> Thanks a lot! ^:)^ In fact, I’ve been trying to understand with this your blog-post about coroutines and I have already a similar code using such features to compare with. More about this soon.
¡Saludos! By the way: your Spanish is good :)>-

8

@quezadav - Dolor comunicado, dolor alviado* :slight_smile:

*(thank you, Google)