Question

I have a module with the following subroutines:

package module;

sub new
{
    my $class = shift;
    my $reference = shift;
    bless $reference, $class;
    return $reference;
};

sub add_row{

    @newrow = [1,1,1];
    push @_, @newrow;

};

@matricies is an array of array references. I created objects out of the array references using

my @object= map{module->new($_)} @matrices;

and lets say I want to add a row to one of the objects using:

@object[0]->add_row();

I think there’s something wrong with the add_row subroutine dealing with the use of @ and $. Any ideas?

Answer 1

Yes, you are adding an array ref yet your variable is an array.

The first thing you need to do (after using strict and warnings) is to read the following documentation on sigils in Perl (aside from good Perl book):

• https://stackoverflow.com/a/2732643/119280 – brian d. foy’s excellent summary

• The rest of the answers to the same question

• This SO answer

The best summary I can give you on the syntax of accessing data structures in Perl is (quoting from my older comment)

• the sygil represents the amount of data from the data structure that you are retrieving ($ of 1 element, @ for a list of elements, % for entire hash)

• whereas the brace style represent what your data structure is (square for array, curly for hash).

---

Now, for your code:

@newrow = [1,1,1];
push @_, @newrow;

should be

my $newrow = [1,1,1];
push @_, $newrow;

You have another problem in how to access your rows from the object:

sub add_row {
    my ($self, $newrow) = @_;
    $newrow ||= [1,1,1]; # In case it wasn't passed, default to this?
    push @{$self}, $newrow;
};

You also have the same problem with @object[0]->add_row(); as with newrow – you are using array sigil to address 1 element

$object[0]->add_row(); # will add default row of [1,1,1]
$object[0]->add_row([2,3,4]);

---

UPDATE: here’s a complete code:

Module’s add_row() (your constructor is fine):

sub add_row {
    my ($self, $newrow) = @_;
    $newrow ||= [1,1,1]; # In case it wasn't passed, defauly to this?
    push @{$self}, $newrow;
};

Test driver:

use a1;
my @objects = (a1->new([[5,6,7],[8,9,10]]));
$objects[0]->add_row();
$objects[0]->add_row([3,4,5]);
use Data::Dumper; print Data::Dumper->Dump([\@objects]);

Results:

$VAR1 = [
      bless( [
               [
                 5,
                 6,
                 7
               ],
               [
                 8,
                 9,
                 10
               ],
               [
                 1,
                 1,
                 1
               ],
               [
                 3,
                 4,
                 5
               ]
             ], 'a1' )
    ];