sub set_foo {
  my ($self, $newfoo) = @_;
  $self->[1] = localtime(); # track last change
  $self->[0] = $newfoo;
  $self->_recalculate_bar();
}

sub get_foo {
  $self->[2] = localtime(); # track last access
  return $_[0]->[0];
}

##</code><code>##

$slick->{foo} = 'Some value';
print $slick->{foo}, "\n";

##</code><code>##

$slick->set_foo('Some value');
print $slick->get_foo(), "\n";

##</code><code>##

sub STORE {
  my ($self, $key, $val) = @_;
  # assuming this class has more than just 'foo'...
  unless (grep { $_ eq $key } @CLASS_KEYS ) {
    croak (ref $self) . "has no $key member";
  }

  if ($key eq 'foo') {
    $self->[1] = localtime(); # track last change
    $self->[0] = $val;
    $self->_recalculate_bar();
  } else {
    # set normal keys somehow
  }

}

sub FETCH {
  my ($self, $key, $val) = @_;
  # assuming this class has more than just 'foo'...
  unless (grep { $_ eq $key } @CLASS_KEYS ) {
    croak (ref $self) . "has no $key member";
  }

  if ($key eq 'foo') {
    $self->[2] = localtime(); # track last access
    return $self->[0];
  } else {
    # get normal keys somehow
  }
}