Moose example

moose.pl

#!/usr/bin/env perl

use strict;
use warnings;

use 5.010;

use Net::AFP::DSI::Attention;

my $dsi_attn = Net::AFP::DSI::Attention->new(
    flags => $Net::AFP::DSI::REPLY,
    error_or_offset => 106,
    request_id => 1234,
    payload => 'butts',
);

say $dsi_attn->pack

Net::AFP::DSI.pm

package Net::AFP::DSI;

use Const::Fast;
use Moose;

const our $REQ => 0x0;
const our $REPLY => 0x1;

const our $CLOSE => 0x1;
const our $CMD => 0x2;
const our $STAT => 0x3;
const our $OPEN => 0x4;
const our $TICKLE => 0x5;
const our $WRITE => 0x7;
const our $ATTN => 0x8;

has 'flags' => (
    is => 'rw',
    isa => 'Int',
);

has 'command' => (
    is => 'rw',
    isa => 'Int',
);

has 'request_id' => (
    is => 'rw',
    isa => 'Int',
);

has 'error_or_offset' => (
    is => 'rw',
    isa => 'Int',
);

has 'data_length' => (
    is => 'ro',
    isa => 'Int',
    default => 'payload_length',
    lazy => 1,
);

sub has_payload {
    my $self = shift;
    return $self->meta->has_attribute('payload');
}

sub payload_length {
    my $self = shift;
    return length $self->payload if $self->has_payload;
    return 0;
}

1;

Net::AFP::DSI::Attention.pm

package Net::AFP::DSI::Attention;

use Moose;

extends 'Net::AFP::DSI';
with 'Net::AFP::HasPayload';
with 'Net::AFP::Packer';

use constant pack_string => 'C2nN3a*';

sub BUILD {
    my $self = shift;

    $self->command($Net::AFP::DSI::ATTN);
}

1;

Net::AFP::DSI::HasPayload.pm

package Net::AFP::DSI::HasPayload;

use Moose::Role;

has 'payload' => (
    is => 'rw',
    isa => 'Str',
    trigger => sub {
        my $self = shift;
        $self->meta->find_attribute_by_name('data_length')->set_value($self, $self->payload_length);
    },
);

1;

Net::AFP::Packer.pm

package Net::AFP::Packer;

use Moose::Role;
use 5.010;

requires 'pack_string';

sub pack {
    my $self = shift;
    my @attrs;

    foreach my $attr ($self->meta->get_all_attributes) {
        $attrs[$attr->insertion_order] = $attr->get_value($self);
    }

    push @attrs, 0; # filler
    if ($self->has_payload) {
        push @attrs, $self->payload;
    }

    return pack $self->pack_string, @attrs;
}

1;