Lua - nils in table constructor

Question

I have a following code:

local ta = { nil, nil, nil, 1, a = 2 }
local tb = { [4] = 1, a = 2 }

for i = 1, #ta do
  print('ta['..i..']= ', ta[i])
end
for i = 1, #tb do
  print('tb['..i..']= ', tb[i])
end

And get the following output:

ta[1]=  nil
ta[2]=  nil
ta[3]=  nil
ta[4]=  1

I assumed that both tables should be the same. But it's not quite.

I try create table with empty constructor, and initialize elements one by one, including nils at the beginning. But got the same result with the table tb.

What the difference? Can I manage this manually?

Answer 1

In Lua the behaviour of length operator # is undefined for arrays, where sequence is broken, that is, it doesn't start at 1 or has empty slots inside.