I've been tinkering with combinations of strings from different arrays, and discovered that the ubiquitous glob solution breaks for long input strings.

Update: The below example is for Strawberry Perl 5.16.1 on Windows. On Ubuntu 10.4, Perl 5.10.1 (i486-linux-gnu-thread-multi), it first breaks at 4027.

Here's a trivial example to show the effect: 

#!/usr/env/perl

use strict;
use warnings;

my $q = (shift or 129); 
my @x = ( 'A' x $q, 'B' x $q );

my $glob = '{' . join(',', @x) . '}';

while (my $g = glob($glob)) {
    print "$g\n"; # no output if $q > 129
}

##### returns nothing with 129 ####

[download]

What I really want to do is more like this, but glob also fails when longer strings are used: 

my @x = (1..10);
my @y = qw(one two three four five six seven eight nine ten);
my @z = qw(Amy Bob Cal Deb Eck Fay Gin Hob Ian Jan);

my @xyz = (\@x, \@y, \@z);
my $glob = join( ',', map { '{' . join( ',', @$_ ) . '}' } @xyz );

[download]

Q1: Why does glob quietly fail?

Q2: Is there a built-in, core, or module that is not so limited?

Instead of that, I suspect I'll have to do something like the following. This is very simplistic, but does the job. (I'm sure this has been done before, but I haven't spent enough time searching.)

Q3: Any comments here? 

sub make_combo_iter
{
    my $array_ref = shift;
    
    # last index of top level
    my $size = scalar( @{$array_ref} );
    
    # create array of last indices
    my @array_limits;
    for my $i (0..$size-1)
    {
        $array_limits[$i] = scalar( @{$array_ref->[$i]} ) - 1;
    }
    
    # one counter for each sub-array
    my @array_counter = (0) x $size;
    my $done = 0;
    my $iter = sub { 
        if ($done)
        {
            $done = 0;
            return undef;
        }
         
        my @next_combo;
        # compute @next_combo
        for my $i (0..$size-1)
        {
            push @next_combo, $array_ref->[$i][$array_counter[$i]];
        }
         
        # increment counters, set $done if the last one rolls over
        my $rollover = 0;
        for my $c (0..$size-1)
        {
            if (++$array_counter[$c] > $array_limits[$c])
            {
                $array_counter[$c] = 0; # reset
                $rollover = 1;          # carry
            }
            else
            {
                $rollover = 0;  # no carry
                last;           # no more increments
            }
        }
        
        # if the last array rolled over, set the done flag
        if ( $rollover )
        {
            $done = 1;
        }
         
        return \@next_combo;
    }; # anonymous iterator sub
    return $iter;
} # make_combo_iter

[download]

-QM
--
Quantum Mechanics: The dreams stuff is made of

In reply to glob quietly fails by QM

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