Thank you boftx, but this sadly didn't work. new() is the most common constructor but in Perl constructor functions can be named differently AFAIR. MooX seems to have no new()...

According to the documentation and the working examples, the MooX struct could be initialized by

my $dno = Dirnode["", undef];
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but undef yields an error message and I don't know how a zero-element array could be specified in another way. So I did the init with an empty list which works except for the array variables.

So maybe my question should be better asked as "how to initialize a zero-element array?" perhaps?

You could create with an empty array reference instead of undef:

my $dno = Dirnode[$curpath, []];

Good call, Loops. I was thinking of his question in literal terms when he asked about initializing an array and completely overlooked initializing the array ref in the struct.

You must always remember that the primary goal is to drain the swamp even when you are hip-deep in alligators.

Check this link: http://api.metacpan.org/source/BOFTX/Games-Dukedom-v0.1.1/lib/Games/Dukedom.pm

You will see where I use MooX::Struct and later initialize an attribute with StructName->new; in several places.

You can specify a zero-element array with my @array = ();. However, I seem to recall that if you do not provide a value for an attribute in MooX::Struct the element is not created and is in fact undef. But you are using the accessor in your push statement so that shouldn't be a problem.

If I get a break from the kids tonight I'll run your code and see what I can find. (No promises on Halloween, though.)

Update: The actual CPAN docs (which include the module source and an executable) can be found here if you're interested: Games::Dukedom

You must always remember that the primary goal is to drain the swamp even when you are hip-deep in alligators.

Thank you Loops and boftx!

Using the constructor for empty array as Loops showed, the script indeed ran without spewing errors.

I have looked a bit into the long script boftx pointed me at. It really remembers me of a game I liked much on old Apple II :) Many interesting Perl details, in a well-readable script. Not one of these cryptic examples in the docs... But I'll look at it tomorrow when I am not tired as now.

However, when trying to output the contents of the collected directory tree structures, I ran into another problem after adding a sub for this. I get an error "Global symbol "$mydir" requires explicit package name..." which I do not yet understand, as this is a my variable of a subroutine... Please excuse if I made an obvious blatant mistake :(

use strict;
use warnings;
use diagnostics;
use 5.014;  # so push/pop/etc work on scalars (experimental)

use MooX::Struct -rw, Dirnode => [ qw( $dirname @subdlist ) ];
my $dirroot = crawldir( ".");
printdirs ($dirroot);

sub printdirs {
    my $mydir = $_;
    
    # if subdirectories exist, walk them first
### vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv PROBLEM
    if (@($mydir->subdlist)) {
#    if ($mydir->subdlist) {
### ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PROBLEM
        foreach ($mydir->subdlist) {
            printdirs( $_);
        }
    }
    print "Dir: ", $mydir->dirname, "\n";
}

sub crawldir {
    my $curpath = shift;
    my $dno = Dirnode["", []];
#   my $dno = Dirnode->new();
    $dno->dirname( $curpath );

    opendir(DIR, $curpath);
    my @files = readdir(DIR);
    closedir(DIR);
    print "crawldir in directory ", $dno->dirname, "\n";
    foreach (@files) {
        next if $_ eq '.' or $_ eq '..';
        my $file_path = "$curpath/$_";
        $file_path =~ s|/+|/|g;
        if (-d $file_path) {
           print "crawldir in directory ", $dno->dirname, ": calling c
+rawldir( $curpath\/$_)\n";
           push @{$dno->subdlist}, crawldir( "$curpath\/$_" );
        }
    }
    return $dno;
}
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