Re: ipairs parameters

[Thijs Schreijer <thijs@...>]

> On 20 Jun 2016, at 19:06, Dirk Laurie <dirk.laurie@gmail.com> wrote:
> 
> 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.
> 

Indeed, a (very small) backward compatibility issue. But this same caveat is already present in many locations.