Question

I want to define an array as attribute of a class and fill it with some data when the class is instantiated.

I thought it would be possible to use a $self->attribute->set($id, $value) method in order to set an element on a given index. At least that’s what I understood from the Moose documentation.

But when I try

use Data::Dumper qw( Dumper );
use Moose;

has cells => (
    is => 'rw',
    traits  => ['Array'],
    isa     => 'ArrayRef',
    default => sub { [] },
);

my $app = __PACKAGE__->new();
$app->cells->set($_, $_) for 0..3;
print(Dumper($app->cells));

I get

Can't call method "set" on unblessed reference

How can I do I make set work?

Answer 1

use Data::Dumper qw( Dumper );
use Moose;

has cells => (
    is => 'rw',
    traits  => ['Array'],
    isa     => 'ArrayRef',
    default => sub { [] },
    handles => {                   # <---
       set_cell => 'set',          # <---
    },                             # <---
);

my $app = __PACKAGE__->new();
$app->set_cell($_, $_) for 0..3;   # <---
print(Dumper($app->cells));

---

Despite claims to the contrary in the comments, it works fine in BUILD too.

use Data::Dumper qw( Dumper );
use Moose;

has cells => (
    is => 'rw',
    traits  => ['Array'],
    isa     => 'ArrayRef',
    default => sub { [] },
    handles => {
       set_cell => 'set',
    },
);

sub BUILD {
    my ($self) = @_;
    $self->set_cell($_, $_) for 0..3;
}

my $app = __PACKAGE__->new();
print(Dumper($app->cells));