Helping with hashes

package Class;
use Moose;
use MooseX::AttributeHelpers;

has 'name_birthdate_map' => (
    metaclass => 'Collection::Hash',
    is        => 'ro',
    isa       => 'ArrayRef[DateTime]',
    provides  => {
       keys   => 'names',
       values => 'birthdates',
       count  => 'name_count',
       empty  => 'has_names',
    },
);

my $c = Class->new( name_birthdate_map => { 'Some Person' => DateTime->now } );
$c->names; # ('Some Person')
$c->birthdates; # ('2008-03-26T01:30')
$c->count; # 1