How to use ArrayRef[Class] in Moose

Question

Sorry for a bit long code, but want provide an nearly working example.

package MLQ::Jobs::Job {
    use 5.016;
    use Moose;
    use warnings;
    has 'name' => (is=>'rw', isa=>'Str');
    has 'status' => (is=>'rw', isa=>'Str');
}

package MLQ::Jobs {
    use 5.016;
    use Moose;
    use warnings;
    #use MLQ::Jobs::Job;

    has jobs => (
        is => 'rw',
        isa =>'ArrayRef[MLQ::Jobs::Job]',     #jobs - an array of zero to many jobs
        builder => '_scan_jobs',              #initializing it when creating the object Jobs
    );

    sub _scan_jobs {
        my $self = shift;
        #test code
        foreach my $i (1..10) {
            my $j = MLQ::Jobs::Job->new();
            $j->name("name $i");
            $j->status("stat $i");
            push @{$self->{jobs}}, $j;
        }
    }
}

package main {
    use 5.016;
    use warnings;
    use Data::Dumper;
    #use MLQ::Jobs;
    my $j = MLQ::Jobs->new();
    say Dumper $j;
}

When running the above code, got an 10 lines long error message What is NOT helpfull at all. At least not helpful for an casual perl programmer - like me... :( Understand the 1st line, but can't find the error in the code...

Attribute (jobs) does not pass the type constraint because: Validation failed for 'ArrayRef[MLQ::Jobs::Job]' with value  at /Users/me/perl5/perlbrew/perls/perl-5.16.3/lib/site_perl/5.16.3/darwin-2level/Moose/Meta/Attribute.pm line 1289.
        Moose::Meta::Attribute::verify_against_type_constraint('Moose::Meta::Attribute=HASH(0x7fce1082ec78)', '', 'instance', 'MLQ::Jobs=HASH(0x7fce1082a378)') called at /Users/me/perl5/perlbrew/perls/perl-5.16.3/lib/site_perl/5.16.3/darwin-2level/Moose/Meta/Attribute.pm line 1276
        Moose::Meta::Attribute::_coerce_and_verify('Moose::Meta::Attribute=HASH(0x7fce1082ec78)', '', 'MLQ::Jobs=HASH(0x7fce1082a378)') called at /Users/me/perl5/perlbrew/perls/perl-5.16.3/lib/site_perl/5.16.3/darwin-2level/Moose/Meta/Attribute.pm line 546
        Moose::Meta::Attribute::initialize_instance_slot('Moose::Meta::Attribute=HASH(0x7fce1082ec78)', 'Moose::Meta::Instance=HASH(0x7fce1082f4a0)', 'MLQ::Jobs=HASH(0x7fce1082a378)', 'HASH(0x7fce1082a360)') called at /Users/me/perl5/perlbrew/perls/perl-5.16.3/lib/site_perl/5.16.3/darwin-2level/Class/MOP/Class.pm line 525
        Class::MOP::Class::_construct_instance('Moose::Meta::Class=HASH(0x7fce108372a8)', 'HASH(0x7fce1082a360)') called at /Users/me/perl5/perlbrew/perls/perl-5.16.3/lib/site_perl/5.16.3/darwin-2level/Class/MOP/Class.pm line 498
        Class::MOP::Class::new_object('Moose::Meta::Class=HASH(0x7fce108372a8)', 'HASH(0x7fce1082a360)') called at /Users/me/perl5/perlbrew/perls/perl-5.16.3/lib/site_perl/5.16.3/darwin-2level/Moose/Meta/Class.pm line 274
        Moose::Meta::Class::new_object('Moose::Meta::Class=HASH(0x7fce108372a8)', 'HASH(0x7fce1082a360)') called at /Users/me/perl5/perlbrew/perls/perl-5.16.3/lib/site_perl/5.16.3/darwin-2level/Moose/Object.pm line 28
        Moose::Object::new('MLQ::Jobs') called at moo2.pl line 38

Answer 1

The issue is that builder methods, like default, are supposed to return the value to be put in the attribute, not initialize the attribute itself. You'd do that in a BUILD method.

sub _scan_jobs {
    my $self = shift;

    my @jobs;
    foreach my $i (1..10) {
        my $j = MLQ::Jobs::Job->new();
        $j->name("name $i");
        $j->status("stat $i");
        push @jobs, $j;
    }

    return \@jobs;
}