Hi Uri (and all),
On Fri, 14 Mar 2014 13:40:02 -0400
Uri Guttman <u...@stemsystems.com> wrote:
> On 03/14/2014 01:03 PM, Ralph Grove wrote:
> > I'm trying to determine how Perl evaluates operands for expressions. I
> > expected the following code to output 3, 4, and 5, as it would if
> > executed as a C++ or Java program. The actual output that I get
> > (v5.16.2), however, is 4, 4, and 5. This leads me to believe that
> > operand evaluation is either non-deterministic and compiler-dependent,
> > or it's simply broken.
> >
> > The Perl documentation discusses operator evaluation, but doesn't
> > directly address operand evaluation order. Does anyone know of a good
> > resource for this information?
>
> perl doesn't guarantee any evaluation order. when doing side effects
> like this don't expect any particular result unless you control things
> explicitly.
>
> lists of args passed to subs and ops are evaluated left to right. that
> can be useful if you really want to control evaluation order.
>
> >
> > Thanks,
> > Ralph
> >
> >
> >
> > sub doit {
> > return ++$g ;
> > }
> >
> > $g = 0;
> > my $sum = $g + doit() + doit();
>
> use List::Util qw( sum ) ;
>
> my $sum = sum( $g, doit(), doit() ) ;
>
> that will do what you think it should do.
>
> since + officially doesn't care about left to right ordering, perl does
> what it thinks will be efficient. it can't tell doit() is modifying $g.
>
> but even better DON'T code that way!! even if order was specified that
> is a very dangerous action at a distance piece of code.
>
> uri
Thank you for replying before me, with what I had to say (that the code was too
clever for its own good) and more. Like the old aphorism goes: “Always write
your code, as if the maintenance is a violent psychopath who knows where you
live.”. Avoid overly clever code, that may try to do more in less code.
Shabbath Shalom and happy upcoming https://en.wikipedia.org/wiki/Purim everone
(or just have a great weekend).
Regards,
Shlomi Fish
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