As Perl novice I am trying to learn how I can use structs in Perl. In my last question I got some good hints and now I am trying to do this using MooX instead of Class::Struct.

So far it looks quite straightforward to me, not as awkward like most other approaches. However, I surprisingly ran into a problem. Apparently one needs to explicitly declare structs as read/write. Structs in Perl seem by default like constants. Now the big question is how to achieve this.

Here the script that I try to run with perl -w. The script fails with the message: "tags is a read-only accessor at (eval 129) line 17." I have marked line 17 and as you see, it is empty... 

use strict;
use warnings;
use MooX::Struct Document => [ qw($fileID $filename @tags) ];
    Document  => [ tags => [ is => 'rw', required => 1 ] ];
# the line above produces...
# Useless use of a constant ("Document") in void context at testmoo.pl
+ line 5.
# Useless use of anonymous list ([]) in void context at testmoo.pl lin
+e 5.
# ...instead of making the struct members writeable

my @doc_list;

# simulate processing two files "by hand" for testing
# first document
my $filenumber = 1;
my $filename = "PetsFile";
my @filetags;
# create, allocate and store struct in doc_list
my $doc = Document[ $filenumber, $filename, @filetags];
push @doc_list, $doc;
# <-- this is line 17, and the script fails with the message:
#     tags is a read-only accessor at (eval 129) line 17.
# second document
++$filenumber;
$filename = "BirdsFile";
# create, allocate and store struct in doc_list
my $doc = Document[ $filenumber, $filename, @filetags];
push @doc_list, $doc;

# simulated processing in a later pass
# - this involves modifying struct members after creation
my $tag = "Cats";
push @filetags, $tag;
$tag = "Dogs";
push @filetags, $tag;
$doc_list[1]->tags ( @filetags);
my @filetags;               # new my frees variable and resets to unde
+f again
$tag = "Doves";
push @filetags, $tag;
$tag = "Eagles";
push @filetags, $tag;
$tag = "Shantaks";
push @filetags, $tag;
$doc_list[2]->tags ( @filetags);

# finally check whether this worked as intended
for (1..2) {
#  my $$doc_pointer = \@doc_list[ @_ ];
# mmh a pointer/hard ref would be nice...
# could then avoid to use the index as in the code below...
# need to learn how to do this
  printf "File ID:  %s\n", $doc_list[ @_ ]->fileID;
  printf "Filename: %s\n", $doc_list[ @_ ]->filename;
  printf "Tags:     %s\n", join(', ', @{ $doc_list[ @_ ]->tags });
}

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Does anybody have an idea what I could have done wrong?

In reply to How can I make struct members writeable using MooX::Struct? by dissident

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