Your problem is that $PATTERN in new() is considered a package variable (as it hasn't been declared lexically) so new() is looking up $Thingy::PATTERN and, understandably, is not finding it. A possible solution would be to implement your derived class constructors like so

{
  package Rubber;

  @ISA     = qw( Thingy );
  $PATTERN = q( ... );

  sub new {
    local $Thingy::PATTERN = $PATTERN;
    $_[0]->SUPER::new(@_[1 .. $#_]);
  }
}
[download]

HTH

_________
broquaint