Moose and Roles method modifers

Question

It is possible to use an after modifier in a Role for a required attribute that is populated in the consuming class via a builder method?

package A::Role;
use Moose::Role;
use IO::File;
use Carp;

requires 'properties_file';

after 'properties_file' => sub {
     my $self = shift;

     $self->_check_prop_file();
     $self->_read_file();
};

Consuming class:

    package A::B::C;
    use Moose;
    use Carp;
    use Moose;
    use Carp;
    use HA::Connection::SSH;
    use constant {
     ...
    };

    has 'properties_file' => ( is  => 'ro',
                               isa => 'Str',
                               builder => '_build_current_data');

    with 'A::Role';
    sub _build_current_data { ... }

what are you trying to achieve? what would `_read_file()` do? — stevenl, Feb 18 '13 at 13:30

score 0 · Accepted Answer · answered Feb 18 '13 at 17:03

To answer your question: Yes you can. You've already done the crucial part which was to consume the role after declaring the attribute so that the accessor method is generated.

So the code that you supplied would execute in the sequence that you would expect:-

my $c = A::B::C->new;
# 'properties_file' is built by _build_current_data()

my $filename = $c->properties_file;
# _check_prop_file() and _read_file() are executed (but before $filename is assigned)

However, it does seem strange that you invoke the checking and reading of the properties file by getting properties_file. If you just want the properties file to be checked and read automatically after construction, the role could supply a BUILD method to be consumed into the class. (BUILD is executed after construction, so properties_file will be initialised already.)

sub BUILD {
    my $self = shift;
    $self->_check_prop_file();
    $self->_read_file();
    return;
}

Moose and Roles method modifers

1 Answers1