why lua kv pairs is sequence when key is table

Question

local a = {d = 1}
local b = {d = 2}
local test = {}

test[b] = true
test[a] = true

newtest = {
  d = 1,
  c = 2
}
for i in ipairs(test) do
  print(i.d)
end

for k, v in pairs(newtest) do
  print(k, v)
end

**so why the print of test is in order but the newtest is not every time?

The first loop never does anything. test has no array elements, so ipairs returns an empty iterator. — Nicol Bolas

Piglet Piglet · Accepted Answer · 2020-07-30T06:06:15

From the Lua 5.3 Reference Manual 6.1 Basic Functions: ipairs

ipairs (t) Returns three values (an iterator function, the table t, and 0) so that the construction

for i,v in ipairs(t) do body end

will iterate over the key–value pairs (1,t[1]), (2,t[2]), ..., up to the first nil value.

So ipairs won't work for test as test is not a sequence starting at index 1. It only has two keys which are tables.

why lua kv pairs is sequence when key is table

1 Answers