{
  my %cache;
  sub heavy_lifting {
    my $arg = shift;
    return
      defined $cache{ $arg } ? $cache{ $arg }
                             : $cache{ $arg } = grunt($arg);
}

##</code><code>##

sub heavy_lifting {
  my $self = shift;
  my $arg = shift;
  return defined $self->{ _heavy } ? $self->{ _heavy }
                                   : $self->{ _heavy } = $self->grunt( $arg );
}