Basic questions about tables

Sun, 30 Jan 2022 16:38:24 UTC

Hey, hello! I'm a beginner in programming. I followed the tutorial "Game Development using PICO-8 by Dylan Bennett" to learn to use Pico-8. follow the page 28 of the tutorial. I wrote a game which just like "Flappy Bird", and then I ran into some questions about "tables".

The questions are as follows:
I don't understand what the means about"cave={{["top"]=5,["btm"]=119}}".

The context of this code is as follows（In line 2）：

function make_cave()
    cave={{["top"]=5,["btm"]=119}}
    top=45
    btm=85
end

function update_cave()
    if (#cave>player.speed) then
        for i=1,player.speed do 
        del (cave,cave[1])
        end
    end

    while (#cave<128) do
    local col={}
    local up=flr(rnd(7)-3)
    local dwn=flr(rnd(7)-3)
    col.top=mid(3,
    cave[#cave].top+up,top)
    col.btm=mid(btm,
    cave[#cave].btm+dwn,124)
    add(cave,col)
    end

end

function draw_cave()
    top_color=5
    btm_color=5
    for i=1,#cave do
        line(i-1,0,i-1,cave[i].top,
        top_color)
        line(i-1,127,i-1,cave[i].btm,
        btm_color)
    end
end

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Basic questions about tables