Dear Perlmonks, I have to ask for your wisdom. I am currently writing a OO-Module in Mouse and came into trouble using predicates.

The Situation is as follows:
My Module is an extension to an already existing (huge legacy) deamon, written in procedural perl. This deamon instantiates an object of my Class and hands over a parameter hash in the constructor, to fill the objects accessors. Like this:

\%data = { customer_number => $custno, country => $country, ticket_typ
+e => $ticketsystem };
$test_class = "Utils::Testclass::MyTest"->new($data);
<\code>

<p>Utils::Testclass::MyTest has correspondig accessors like this:</p>

<code>
has 'customer_number' => (
    is        => 'rw',
    reader    => 'get_customer_number',
    writer    => 'set_customer_number',
    predicate => 'has_customer_number',
    clearer   => 'clear_customer_number',
);
has 'country' => (
    is        => 'rw',
    reader    => 'get_country',
    writer    => 'set_country',
    predicate => 'has_country',
    clearer   => 'clear_country',
);
has 'ticket_type' => (
    is        => 'rw',
    reader    => 'get_ticket_type',
    writer    => 'set_ticket_type',
    predicate => 'has_ticket_type',
    clearer   => 'clear_ticket_type',
);
[download]

I wish to test if my accessors are set using my perdicate e.g. $self->has_country and based on which accessors are set the module does some internal magic. So far, nothing special, but my code did not work. Then I found this gem in the deamons code, which replaces all values which are undef with empty strings and kills my usage of predicates:

map {  $data{$_} = '' unless defined $data{$_} } keys %data;
[download]

Note: It is not possible for me to change the code of the deamon. That program expects the empty string several times and I do not have permission to change that.


What can I do to get my predicates working under these conditions?

I already had the following ideas:

1. performing if( not definded($self->get_country) || $self->get_country eq ''). Works, but is far from elegant and not the Mouse/Moose-OO-way. I'd prefer to use the predicate.
2. I thought of the following trigger, to check my values before writing them to the accessor and eventually calling the clearer:
   

   has 'country' => (
       is        => 'rw',
       reader    => 'get_country',
       writer    => 'set_country',
       predicate => 'has_country',
       clearer   => 'clear_country',
       trigger   => sub {
                    my ($self)  = @_;
                        if ( $self->get_country eq '' || not defined($sel
   +f->get_country) ) {
                            $self->clear_country;
                        }
                    }
   );
   [download]

   This is much more the direction that I want and I can use the predicate. However: I have to copy the exact same trigger method for every accessor, changing only the name of the get and clear methods. I really don't like this duplicate code, as there are going to be more accessors like these in the future.

Dear Perlmonks, do you have a more elegant idea on this topic? Anything with less duplicate code not throwing overboard the Mouse-OO-way?

I appreciate your thoughts,
Yulivee