Perl OOP method returns array I cannot loop

Question

Here is what my module looks like:

#!/usr/bin/perl
package Page;

use strict;
use warnings;

use base qw/DBObj/;

our %fields = (
  id => undef,
  title => '$',
  content => '$'
);

sub get_field_names {
  my @names = sort keys \%fields;

  return \@names;
}

for my $field ( keys %fields ) {
  my $slot = __PACKAGE__ ."::$field";
  no strict "refs";

  *$field = sub {
    my $self = shift;
    $self->{$slot} = shift if @_;
    return $self->{$slot};
  }
}

1;

Here the parent module where the strange behaviour occurs

#!/usr/bin/perl
package DBObj;

use strict;
use warnings;

use Data::Dumper;

use DBConn;

sub new {
  my $me = shift;
  my $class = ref $me || $me;

  my $self = {
    dbh => new DBConn->new(
        dns => '/db.sql',
        user => '',
        pass => '',
      )
  };

  return bless $self, $class;
}

sub save {
  my $self = shift;

  my @field_names = @{$self->get_field_names};

  print Dumper @field_names;

  foreach my $item ( reverse @field_names ) {
    print $item;
  }
}
sub fill {
  my ( $self, $args ) = @_;

  foreach my $key ( keys $args ) {
    $self->$key( $args->{$key} );
  }
}

1;

here is what I am experiencing. This snippet

my @field_names = $self->get_field_names;

print Dumper @field_names;

foreach my $item ( reverse @field_names ) {
    print $item;
}

Data::Dumper shows

$VAR1 = [
          'content',
          'id',
          'title'
        ];

But the foreach loop returns

ARRAY(0x7fc750a26470)

I have a Test::Simple test case where I perform the following test

ok( shift $page->get_field_names eq 'content', 'Page has field content');

so I can shift off an item from the array, but I cannot loop through it which is a puzzle to me.

And please; before you tell me that I shouldn't be doing this and that there is a ton of modules out there I should pick instead, I want to point out; I am doing this our of pure fun, I have been away from Perl for ~10 years and thought it would be fun to play around with it again.

TobyLL · Accepted Answer · 2015-02-18 18:19:47Z

7

You have made get_field_names return a reference to an array, but you are then putting that reference into an array variable.

Try:

my $field_names = $self->get_field_names;

print Dumper $field_names;

foreach my $item ( reverse @$field_names ) {
    print $item;
}

answered Feb 18, 2015 at 18:19

TobyLL

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3 Comments

kristian nissen Over a year ago

this results in the following "Global symbol "$field_names" requires explicit package name at ../modules/DBObj.pm line 34." that's not working out of the box

TobyLL Over a year ago

Which line of the above is line 34 in your script? Did you change my @field_names = ... to my $field_names = ...?

kristian nissen Over a year ago

Sorry, I made a mistake when I altered my code. Your example works

jwodder · Accepted Answer · 2015-02-18 18:19:34Z

1

get_field_names returns an arrayref, not an array. Either change its return type by removing the backslash from return \@names; or "cast" its return type to an array by writing:

my @field_names = @{$self->get_field_names};

answered Feb 18, 2015 at 18:19

jwodder

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2 Comments

Borodin Over a year ago

Perl subroutines cannot return an array, only a list. And that isn't “casting”, it's dereferencing.

kristian nissen Over a year ago

This works, I used @{$self->get_field_names}; and it now prints each item in the array - thanks. If I remove the backslash nothing is being printed inside the foreach

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