package A;
sub new { 
  my $class = shift;
  my $this = bless {}, $class;
  $this->{-twin} = new B(-twin => $this);
  return $this;
}
package B;
sub new {
  my $class = shift;
  bless {@_}, $class;
}
$obj = new A;
undef $obj;

##</code><code>##

package A;
sub new { 
  my $class = shift;
  my $this = bless {}, $class;
  $this->{-twin} = new B(-twin => $this);
  return $this;
}
package B;
sub new {
  my $class = shift;
  my $this = bless {@_}, $class;
  weaken $this->{-twin};
  return $this;
}
$obj = new A;
undef $obj;

##</code><code>##

$bar = "this\nthat\n";
open(FH, '<', \$bar);
$this = <FH>; # reads "this\n"
$that = <FH>; # reads "that\n"
open(FH, '>', \$bar);
print FH "this\n";
print FH "that\n";

##</code><code>##

# $foo = capture { print 'hi'; }
# $foo will be filled as if someone had done $foo = `perl -e { print 'hi'; }` or something like that
# if the sub prints directly to STDOUT, like:  print STDOUT 'hi'; then the output will not be captured
sub capture(&) {
	my ($oldsel, $fh, $ret);
	open($fh, '>', \$ret) or die "can't capture: $!";
	$oldsel = select($fh);
	&{$_[0]};
	select $oldsel;
	close($fh);
	$ret;
}

##</code><code>##

$"=$,,$_=q>|\p4<6 8p<M/_|<('=>
.q>.<4-KI<l|2$<6%s!<qn#F<>;$,
.=pack'N*',"@{[unpack'C*',$_]
}"for split/</;$_=$,,y[A-Z a-z]
         {}cd;print lc