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

[Andrew Starks <andrew.starks@...>]

On Wednesday, September 17, 2014, Coda Highland <chighland@gmail.com> 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.
> >
> > Just going by the 5.2 reference manual, I wouldn't know whether I
> > could depend on #table being 0 for an empty table. I'd have to peek
> > under the hood of each particular Lua implementation, and
> > portability wouldn't be assured.
> >
> > PIL does a better job with this when it says "In particular, a
> > table with no [positive] numeric keys is a sequence with length
> > zero." I think such a direct statement in the normative reference
> > would be very helpful.
> >
> > Anyway, practically speaking, I feel my question has been answered,
> > and I'll continue assuming my empty tables have length zero. :-)
>
> 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.
>
> /s/ Adam

I find the manual to be this way, generally.  It's extremely... efficient.  I'm *almost* smart enough to undrstand things on the first try. 

-Andrew