Moose from ArrayRef[HashRef] to ArrayRef[Object]

saintex has asked for the wisdom of the Perl Monks concerning the following question:

Hello Monks,

Following a previous conversation (for which I thank all the Monks):
href="http://www.perlmonks.org/?node_id=887227

I have started to use MooseX::SimpleConfig to have object constructions from config files.

But I have a problem related to types:
I would like to have an ArrayRef of objects, but I forced to have an ArrayRef of hashes.

How I can force a type to be another one?

Here there is some code, just to have an idea.

I inserted only the essential parts.

YAML FILE:

pages:
- Page:
   URL: http://www.perlmonks.org/

- Page:
   URL: http://www.perl.org/
[download]

Page Class:

package Page;
our $VERSION=0.01;

use Moose; 

has 'URL' => (is => 'ro', isa => 'Str',required => 1);

__PACKAGE__->meta->make_immutable;

1;
[download]

Objects container class (with ArrayRef):

package PagesGenerator;
our $VERSION=0.01;

use Moose; 
with 'MooseX::SimpleConfig';

use Page;


has 'pages'=>(
              is=>'rw',
              isa=>'ArrayRef[Page]',
              default => sub { [ ] },
         );


__PACKAGE__->meta->make_immutable;

1;
[download]

And finally on main script, the object construction:

use strict;
use warnings;
our $VERSION=0.01;

use FindBin qw($Bin);
my $p=PagesGenerator->new_with_config(configfile => "$Bin/pages-temp.y
+aml");
[download]

But, while page is an ArrayRef[Page] I have this error:

Attribute (pages) does not pass the type constraint because: Validatio
+n failed for 'ArrayRef[Page]' with value ARRAY(0x22422e8) at /usr/loc
+al/share/perl/5.10.0/MooseX/ConfigFromFile.pm line 44
    MooseX::ConfigFromFile::new_with_config('PagesGenerator', 'configf
+ile', 'pages-temp.yaml') called at navigator.pl line 14
[download]

If I choose an ArrayRef[HashRef], all works fine.

The problem is that I need exaclty an ArrayRef[Page].

So I could coerce one type in another.
I readed something about coercion in Moose, but I don't understand how to use it in my case.

Any suggestions is welcome.

Thank you!

Comment on Moose from ArrayRef[HashRef] to ArrayRef[Object] Select or Download Code

Replies are listed 'Best First'.
Re: Moose from ArrayRef[HashRef] to ArrayRef[Object] by ikegami (Patriarch) on Feb 23, 2011 at 15:27 UTC
You could create a coerce rule for creating ArrayRef[Page] from ArrayRef[HashRef]. Don't forget `coerce=>1`.	[reply] [d/l]
Re^2: Moose from ArrayRef[HashRef] to ArrayRef[Object] by saintex (Scribe) on Feb 23, 2011 at 16:10 UTC
yes... but... how? I have checked the samples on Moose manual and I am a little confused.	[reply]
Re^3: Moose from ArrayRef[HashRef] to ArrayRef[Object] by ikegami (Patriarch) on Feb 23, 2011 at 18:44 UTC
Using BUILDARGS to avoid effects at a distance: { package Page; use strict; use warnings; use Moose; has 'url' => ( is => 'ro', isa => 'Str', required => 1, ); no Moose; __PACKAGE__->meta->make_immutable(); } { package Container; use strict; use warnings; use Moose; my $pages_constraint = Moose::Util::TypeConstraints::create_paramet +erized_type_constraint('ArrayRef[Page]'); my $aoh_constraint = Moose::Util::TypeConstraints::create_paramet +erized_type_constraint('ArrayRef[HashRef]'); around BUILDARGS => sub { my $orig = shift; my $class = shift; my %args = ( @_ == 1 ? %{ $_[0] } : @_ ); if (exists($args{pages})) { my $pages = $args{pages}; if (!$pages_constraint->check($pages)) { # Need to coerce? if ($aoh_constraint->check($pages)) { # Can we coerce? $args{pages} = [ map Page->new($_), @$pages ]; } } } return $class->$orig(%args); }; has 'pages' => ( is => 'rw', isa => 'ArrayRef[Page]', default => sub { [ ] }, ); no Moose; __PACKAGE__->meta->make_immutable(); } Container->new( pages => [ { url => "a" }, { url => "b" } ] ); [download] This is basically the same approach you tried, but correctly uses the more appropriate BUILDARGS instead of BUILD. Coded so it can take both `ArrayRef[HashRef]` and `ArrayRef[Page]`.	[reply] [d/l] [select]
Re^4: Moose from ArrayRef[HashRef] to ArrayRef[Object] by saintex (Scribe) on Feb 23, 2011 at 22:50 UTC
Re^4: Moose from ArrayRef[HashRef] to ArrayRef[Object] by saintex (Scribe) on Feb 24, 2011 at 09:16 UTC
Re^5: Moose from ArrayRef[HashRef] to ArrayRef[Object] by ikegami (Patriarch) on Feb 24, 2011 at 15:59 UTC
Re^3: Moose from ArrayRef[HashRef] to ArrayRef[Object] by ikegami (Patriarch) on Feb 23, 2011 at 18:23 UTC
{ package Page; use strict; use warnings; use Moose; has 'url' => ( is => 'ro', isa => 'Str', required => 1, ); use Moose::Util::TypeConstraints; subtype 'Pages' => as 'ArrayRef[Page]'; coerce 'Pages' => from 'ArrayRef[HashRef]' => via { [ map __PACKAGE__->new($_), @{ $_[0] } ] }; no Moose::Util::TypeConstraints; no Moose; __PACKAGE__->meta->make_immutable(); } { package Container; use strict; use warnings; use Moose; has 'pages' => ( is => 'rw', isa => 'Pages', coerce => 1, default => sub { [ ] }, ); no Moose; __PACKAGE__->meta->make_immutable(); } Container->new( pages => [ { url => "a" }, { url => "b" } ] ); [download] I don't really like the global-ness of the coercion. I'll be posting an alternative that uses BUILDARGS shortly.	[reply] [d/l]
Re^3: Moose from ArrayRef[HashRef] to ArrayRef[Object] by saintex (Scribe) on Feb 23, 2011 at 17:06 UTC
This is an horrible solution, because of duplicate attributes: YAML file: `tmpPages: - Page: URL: http://www.perlmonks.org/ - Page: URL: http://www.perl.org/` [download] Objects container: `package PagesGenerator; our $VERSION=0.01; use Moose; with 'MooseX::SimpleConfig'; use Page; has 'tmpPages'=>( is=>'rw', isa=>'ArrayRef[HashRef]', default => sub { [ ] }, ); has 'pages'=>( is=>'rw', isa=>'ArrayRef[Page]', default => sub { [ ] }, ); sub BUILD{ my $self=shift; @{$self->pages}= map {new Page(URL=>$$_{Page}{URL});} @{$self->tmp +Pages}; for ( @{ $self->pages } ) { print $_->URL; print "\n"; } }` [download] Any other idea?	[reply] [d/l] [select]


more useful options
	PerlMonks