my $ratio = Sub::ParamObject->new({
    nominator   => qr/^[-+]?\d+$/,
    denominator => sub { $_[1] =~ qr/^\d+$/ and $_[1] != 0 },
  });

  # works and is convenient
  $ratio->nominator(-1);
  $ratio->denominator(1);

  my $source = Sub::ParamObject->new({
    selector   => qr/^filename|url$/,
    filename   => sub {$_->[0]->{selector} eq 'filename' and $_[1] =~ qr/^\w+$/ },
    url        => $_->[0]->{selector} eq 'filename' and $_[1] =~ qr!^https?://!i },
  });

  # and now ???
  # I want to have selector set to one of the values
  # and (only) the corresponding field set.
  $source->selector('filename')->filename('foo.txt'); # works
  $source->filename('foo.txt')->selector('filename'); # cannot in my implementation

##</code><code>##

perl -MHTTP::Daemon -MHTTP::Response -MLWP::Simple -e ' ;    # The  
$d = new HTTP::Daemon and fork and getprint $d->url and exit;#spider
($c = $d->accept())->get_request(); $c->send_response( new   #in the
HTTP::Response(200,$_,$_,qq(Just another Perl hacker\n))); ' #  web