package myclass;
use Carp qw(croak);

sub new {
    my ($class, $value) = @_;

    croak "required value missing" if @_ == 1 or !$value;

    return bless \$value, $class;
}

package mysubclass;
use base qw(myclass);

sub new {
    my ($class) = @_;

    return bless $class->SUPER::new(23), $class;
}