Store a Moose object that has a PDL as an attribute - perl

Question

I am new to Moose and doing quite well until I have hit a snag using a PDL as a property. I want to be able to write an object to a file (I have been using use MooseX::Storage; with Storage('io' => 'StorableFile');, and this object has a PDL as a attribute. PDL::IO::Storable provides the necessary methods to use Storable in this way, however I am at a loss as to how to do this in Moose.
Here is an example, it is a little long, I know, but it is as minimal as I can make it:
#!/usr/bin/perl
package LinearPDL;
use Moose;
use PDL::Lite;
use PDL::IO::Storable;
use MooseX::Storage;
with Storage('io' => 'StorableFile');
has 'length' => (is => 'ro', isa => 'Num', required => 1);
has 'divisions' => (is => 'ro', isa => 'Int', required => 1);
has 'linear_pdl' => (is => 'ro', isa => 'PDL', lazy => 1, builder => '_build_pdl');
sub _build_pdl {
my $self = shift;
my $pdl = $self->length() / ( $self->divisions() - 1 ) * PDL::Basic::xvals($self->divisions());
return $pdl;
}
no Moose;
__PACKAGE__->meta->make_immutable;
use strict;
use warnings;
my $linear_pdl = LinearPDL->new('length' => 5, 'divisions' => 10);
print $linear_pdl->linear_pdl;
$linear_pdl->store('file'); # blows up here!
my $loaded_lpdl = load('file');
print $loaded_lpdl->linear_pdl;
I think I may have to make a PDL type or perhaps even wrap PDL into something (using MooseX::NonMoose::InsideOut), but perhaps someone can save me from that (or point me down the right road if it is).

Answer 1

You don't say what actually goes wrong. At a guess you'll need to tell MooseX::Storage how to handle the PDL object using the PDL object's Storable hooks. The documentation for this feature in MooseX::Storage is very poor but MooseX::Storage::Engine has a add_custom_type_handler() method that takes a typename (PDL in your case) and a HashRef of handlers.
MooseX::Storage::Engine->add_custom_type_handler(
'PDL' => (
expand => sub { my ($data) = #_; ... },
collapse => sub { my ($object) = #_; ... },
)
);
Please swing past #moose on irc.perl.org or the Moose mailing list and ask.
[Edit: Update with an example based on the tests.]

Answer 2

The question by Joel and response from perigrin helped me solve a storage problem that had been sitting in the back of my mind for a while. I'm posting a working example here. It doesn't use PDL but it's related and may help someone in the future.
{
package MVR;
use Moose;
use MooseX::Storage;
use Math::Vector::Real;
use Data::Structure::Util qw (unbless);
with Storage('format' => 'JSON', 'io' => 'File');
MooseX::Storage::Engine->add_custom_type_handler(
'Math::Vector::Real' => (
expand => sub {my $v = shift; Math::Vector::Real->new(#{$v})},
collapse => sub {my $mvr = shift; return (unbless($mvr)) },
)
);
has 'mvr' => (is => 'rw', isa => 'Math::Vector::Real');
1;
}
use Math::Vector::Real;
my $p = MVR->new(mvr => V(0,1,3));
print $p->dump;
$p->store('my_point.json');
my $p1 = MVR->load('my_point.json');
print $p1->dump;