Re: Does PIL (3rd edition) repeatedly misuse the length operator on tables and invoke undefined behavior?

[polyglot@...]

On 2014-09-18 06:48, Coda Highland wrote:
> On Wed, Sep 17, 2014 at 1:01 PM,  <polyglot@openmailbox.org> wrote:
> > On 2014-09-18 05:17, Coda Highland wrote:
> > > The difference between 0 and -42 in the aforementioned loop iteration
> > > is that 0 is a cardinal number (that is, a number that can be used to
> > > describe the size of a set), but -42 is not.
> >
> >
> > That's why 0 makes more sense than -42, but the trouble with undefined
> > behavior is that it's not required to do what makes more sense. The
> > length value of -42 for an empty table seems perfectly consistent
> > with the wording of the 5.2 reference manual.
>
> I'm pretty sure you missed my point. The definition in the 5.2 manual
> DOES explicitly say that an empty table has a length of 0. It doesn't
> special-case it, but that IS a consequence of the definition
> presented. It's not "you can assume it" -- it's "it's guaranteed." The
> wording isn't ambiguous, just complicated.

I disagree.

n = 0 and n = -42 both satisfy the 5.2 reference definition of
a sequence. [1, 0] and [1, -42] in math are both empty sets/intervals.
1,0 and 1,-42 both produce an empty set with the Lua for loop you
originally offered to show why 0 'works'.

The qualification that a length be a cardinal number would indeed
resolve the problem, but this qualification is something *you've*
added. It's not in the 5.2 reference manual, AFAIK. The very fact
that the 5.3 manual adds the "non-negative" qualification for n
suggests that the 5.2 manual is lacking.