I’m a little surprised no-one has suggested a good, old-fashioned, C-style for loop. If speed is a factor, it’s a clear winner over foreach-with-negation:

#! perl
use strict;
use warnings;
use Benchmark qw( cmpthese );

my $n = 1e4;

cmpthese
(
    100,
    {
        foreach_loop => \&foreach_loop,
        c_for_loop   => \&c_for_loop,
    }
);

sub foreach_loop
{
    for my $i (-$n .. 0)
    {
        print -$i;
    }
}

sub c_for_loop
{
    for (my $j = $n; $j >= 0; --$j)
    {
        print $j;
    }
}

[download]

Output (end only):

               Rate foreach_loop   c_for_loop
foreach_loop 89.0/s           --         -69%
c_for_loop    292/s         227%           --

 2:32 >

[download]

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

In reply to Re: counting backward by Athanasius
in thread counting backward by ag4ve

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