Setting a custom hash accessor handle in Moose attribute

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

Dear Monks,

I have written a Moose object module using the following attribute:

package MyObj;

use Moose;
use namespace::autoclean;

# some irrelevant attributes and methods...

has 'custom_fields' => (
    traits  => [qw( Hash )],
    isa     => 'HashRef',
    builder => '_build_custom_fields',
    handles => {
        custom_field        => 'accessor',
        has_custom_field    => 'exists',
        custom_fields       => 'keys',
        has_custom_fields   => 'count',
        delete_custom_field => 'delete',
    },
);

sub _build_custom_fields {
    return {};
}
__PACKAGE__->meta->make_immutable;

1;
[download]

I would like to change the default hash accessor, such that an attempt to read from a non-existing key will croak, while writing (setting) a non-existing key will work as usual. That is:

my $obj =  MyObj->new();
$biorange->custom_field('foo', 23); # OK
my $foo = $biorange->custom_field('foo'); # OK
my $foo = $biorange->custom_field('bar'); # should croak!
[download]

I guess I should replace the accessor with my own code (?), but I'm not sure what interface I should follow (i.e. what is the accessors prototype and how do I get access to the actual hash).

Thank you,
Dave

Comment on Setting a custom hash accessor handle in Moose attribute Select or Download Code

Replies are listed 'Best First'.
Re: Setting a custom hash accessor handle in Moose attribute by stvn (Monsignor) on Oct 24, 2010 at 23:35 UTC
Try this: `before 'custom_field' => sub { my $self = shift; if (scalar @_ == 1) { my $key = shift; confess "The field $key does not exist" unless $self->has_custom_field( $key ); } };` [download] -stvn	[reply] [d/l]
Re^2: Setting a custom hash accessor handle in Moose attribute by daverave (Scribe) on Oct 25, 2010 at 17:27 UTC
Thank you.	[reply]