package Parent;
sub new {
    my $invocant = shift;
    my $class = ref($invocant) || $invocant;
    my $self = {};
    bless $self, $class;
    return $self;
}

package Child;
use base qw(Parent);
sub new {
    # what goes here?
    $self->do_child_specific_stuff();
    return $self;
}