use strict;
use warnings;
use 5.012;

##############
{
    package Point;
    use Moose; # automatically turns on strict and warnings

    has 'x' => (is => 'rw', isa => 'Int');
    has 'y' => (is => 'rw', isa => 'Int');

    use overload
        '""' => \&_stringify;

    sub _stringify {
        state $count;
        my ($rhs, $_lhs, $swap) = @_;

        $count++;

        if ($count < 2) {
            return $rhs;
        }
        else {
            return D->new;
        }
    }

}

################

{
    package Point3D;
    use Moose;
    extends 'Point';

    has 'z' => (is => 'rw', isa => 'Int');
}

###############

{
    package D; use Moose; 
    use overload
        '""' => sub {
                        my $class = ref shift;
                        return "$class|hello"
                    };


}
###############

my $p3d = Point3D->new(x=>10, y=>20);
say "$p3d";
say $p3d->_stringify;


--output:--
Point3D=HASH(0x100bc5078)
D|hello