sub STORE {
  my ($self, $key, $val) = @_;
  # An inline dispatch table
  ({
    foo => sub {
      $self->[1] = localtime(); # track last change
      $self->[0] = $val;
      $self->_recalculate_bar();
    },
    # ...any other keys...
   }->{$key}
   or sub {croak (ref $self) . " has no $key member"}
  )->();
}

sub FETCH {
  my ($self, $key, $val) = @_;
  ({
    foo => sub {
      $self->[2] = localtime(); # track last access
      return $self->[0];
    },
    # ...any other keys...
   }->{$key}
   or sub {croak (ref $self) . " has no $key member"}
  )->();