Re: ipairs parameters

[Dirk Laurie <dirk.laurie@...>]

2016-06-20 16:35 GMT+02:00 Thijs Schreijer <thijs@thijsschreijer.nl>:
> If ipairs would accept start and end indices (like unpack for example) then
> instead of;
>
> for i = 20, 30 do
>   local obj = list[i]
>
>   -- do some stuff with obj
>
> end
>
> I could write;
>
> for i, obj in ipairs(list, 20, 30) do
>
>   -- do some stuff with obj
>
> end
>
> Thoughts? (besides that I could write my own iterator and all the undefined
> stuff for non-contignuous tables etc)

Tampering with either the argument list or the return values of
a standard function is perilous. It is better, if providing such
functionality, to do it under another name.

Suppose a working program that contains the line

for k,v in ipairs(myfunc(x,y,z)) do

where myfunc is a function that returns a table and two more values.
The present behaviour silently discards the extra values.

This modification will cause that program to malfunction.

Moreover, if those two extra values happen to be numbers, the
malfunction may show up only as inexplicable results that require
hours of debugging time.