Index's and keys

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#1 
local x={1,2,3}
x[0] = 5
-- is the x[0] a key or index?
#2

Key, index are interchangeable really. It is just that people like referring to numerical keys as indexes and non-numerical keys as keys. The array part of a table always starts at 1 in Lua(u) so you have a mixed table on your hands. The index 0 gets added to the dictionary part of the table.

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#3

Thank you, are you absolutely certain and an expert, that is what i thought but someone I’m arguing with keeps saying otherwise lol

#5

Also, since arrays in Lua start at 1, if you want to iterate through this table you would need to then use pairs or a numeric for loop starting at zero, since ipairs will only start at one.

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#6

so is it a key or not lul just one word

#7

There is your answer. They are interchangeable really.

#8

no but in that script would it be considered a key or index, the guy I’m talking too keeps saying it’s an index

#9

and only an index (just adding this so i can speak s ssssssssss)

#10

It doesn’t matter, although like I mentioned people just like referring to numerical keys as indexes, anything else as just a “key”.

The index 0 will be added to the dictionary part of the table because Lua arrays start at 1

#11

I’m confused cuz if i use an ipairs() loop on it, it doesn’t print it and ipairs() only prints index’s right?

#12

ipairs only goes through the array part of a table, 0 is not picked up because it is in the dictionary part.

Rough implementation of ipairs in Lua:

function ipairs(a)
    return function(_a, i)
        i = i + 1

        local v = a[i]

        if v ~= nil then
            return i, v
        end
        return nil
    end, a, 0
end
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#13

I think i understand, is it thought of as a index but it’s technically a numerical key?

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#14

pairs will go through every key/value pair in a table, including the 0 index, though as @sjr04 said the 0 isn’t part of the array, so you can’t guarantee that 0 will be printed in order with the rest of the array elements. To ensure the proper ordering of indices you should iterate using a numeric for loop.

local x = {1, 2, 3}
x[0] = 5

for i, v in ipairs(x) do
	print(i, v)
end

--[[
will print:
1 1
2 2
3 3
]]

for i, v in pairs(x) do
	print(i, v)
end

--[[
will probably print:
1 1
2 2
3 3
0 5
]]

for i = 0, 3 do
	print(i, x[i])
end

--[[
will print:
0 5
1 1
2 2
3 3
]]
#15

Actually ipairs{} == ipairs{} is true and if it encounters a nil it returns no value in Lua/Luau so a closer implemention to ipairs would be

local function inext(t, ...)
    if select('#', ...) == 0 then
        error("missing argument #2 (number expected)")
    end
    local i = (...)
    if not tonumber(i) then
        error("invalid argument #2 (number expected, got " .. typeof(i) .. ")")
    elseif type(t) ~= "table" then
        error("invalid argument #1 (table expected, got " .. typeof(t) .. ")")
    end
    i = i + 1
    if t[i] == nil then
        return
    end
    return i, t[i]
end
function ipairs(...)
    if select('#', ...) == 0 then
        error("missing argument #1 (table expected)")
    elseif type((...)) ~= "table" then
        error("invalid argument #1 (table expected, got " .. typeof((...)) .. ")")
    end
    return inext, ..., 0
end