package Package;
use Class::Std;
{
    my %trunk_of    :ATTRS( :get<trunk> init_arg => 'trunk' );

    sub BUILD {
        my ($self, $ident, $arg_ref) = @_;
        return;
    }
}

package Package::Branch;
use base qw(Package);
use Class::Std;
{
    my %branch_of    :ATTRS( :get<branch> init_arg => 'branch' );
    my %trees_of     :ATTRS( :get<trees> );

    sub BUILD {
        my ($self, $ident, $arg_ref) = @_;
        return;
    }
    sub START {
        my ($self, $ident, $arg_ref) = @_;
        $trees_of{$ident}
            = 'lots of '
            . $self->get_branch
            . 'es and'
            . $self->get_trunk
            . 's';
    }
}