18

The following code snippet:

for weight, item in itemlist do
    weight_total=weight_total+weight
end

is causing the error "attempt to call table value" on the first line in that snippet. Why?

Itemlist is a table of tables of weights and strings, like such:

local itemlist = {
                        {4,"weapon_pistol"},
                        {2,"weapon_357"},
                        ...

Nothing is being called as far as I can tell; why is this error coming up?

Jonas
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Schilcote
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1 Answers1

26

The generic for expects 3 arguments: a callable value, some value which is repeatedly passed to it, and the key where the iteration shall start.
Stock lua does not call pairs on the first value passed to for if that's not callable, though some derivatives do.

Thus, you must use ipairs(itemlist), pairs(itemlist), next, itemlist or whatever you want (the last two have identical behavior, and are what most derivatives do).

As an example, an iterator unpacking the value sequence:

function awesome_next(t, k)
    k, t = next(t, k)
    if not t then return end
    return k, table.unpack(t)
end

for k, a, b, c, d in awesome_next, t do
end
Deduplicator
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    So the fixed statement would be `for k, weight, item in pairs(itemlist) do`? – Schilcote Apr 28 '14 at 20:34
  • `next` returns a key-value-pair from the passed table, so more like `for k, v in pairs(itemlist) do`. (I'm now assuming each value `v` contains weight and item...) Anyway, the [standard Lua documentation (5.2)](http://www.lua.org/manual/5.2/manual.html) is quite easily digestible imho... – Deduplicator Apr 28 '14 at 20:37
  • Each value v would be another table containing the weight and item. I'll read the docs. – Schilcote Apr 28 '14 at 20:42