package Baseclass;
# common attributes and methods
sub use_values {
   croak ("Abstract class");
}

package Subclass_1;
use base 'Baseclass';
my @values = (...);
sub use_values { ... }

package Subclass_2;
use base 'Baseclass';
my @values = (...);
sub use_values { ... }

##</code><code>##

package Subclass_1;
use base 'Baseclass';
sub use_values {
   my @values = (...);
   ...
}

##</code><code>##

package Subclass_1;
use base 'Baseclass';
{
  my @values = (...);
  sub use_values { ... }
}