Re: tinsert (was: Finding the version)
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- Subject: Re: tinsert (was: Finding the version)
- From: Edgar Toernig <froese@...>
- Date: 2001年8月13日 21:24:54 +0200
Reuben Thomas wrote:
>
> > Be careful: to correctly implement tinsert in Lua using the C tinsert you must pass the correct number of parameters to the C
> > function, like in
> >
> > function tinsert(t, n, v)
> > if (v) then
> > %tinsert(t, n, v)
> > else
> > %tinsert(t, n)
> > end
> > end
>
> Sorry, I meant that. The version I posted was an incorrect "optimisation"!
Even that is not correct. The original tinsert when called with a nil third
argument will insert that nil into the table. Try:
x={} tinsert(x, 1, nil) print(getn(x))
--> 1
Compatible (fixed) version would be:
function tinsert(t, ...)
if arg.n == 1 then
%tinsert(t, arg[1])
elseif arg.n == 2 then
%tinsert(t, arg[1], arg[2])
else
error("wronger number of args ("..arg.n+1..") for tinsert");
end
end
But that still gives unexpected results for:
tinsert(t, foo()) --> may generate to tinsert(t,a,b)
or
tinsert(t, x, foo()) --> may generate to tinsert(t, x)
when foo does not return the expected number of results.
For a long time I advocate to make C-functions behave similar to
Lua functions regarding argument handling (make missing args nil).
IMHO tinsert has a particularly good example of what can happen...
Ciao, ET.