comment on

What else is great? Here's a couple of my favorites:

Weak references. Ever had interdependent objects? Perl 5.005:
```
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;
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```
The A object formerly referenced by $obj will not go away until the program exits, even after $obj itself is undefed. Why? Because there's a B object that references it. And that B object won't go away because that A object references it too. So it's like the A and B are pointing at each other, keeping each other alive (this is called a circular reference.)
Perl 5.6 added some magic called a 'weak reference'.
```
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;
[download]
```
See the 'weaken'? That specific reference is now "weak", and does not actually add to the reference count (so the only reference to the A object is $obj). When $obj is then undefined, the reference count goes to zero, and any weak references are automatically set to undef by Perl. It's perfect for when you need backreferences that should not keep their referents alive.

Builtin version of IO::Scalar

$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";
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This makes it very easy to convert a function that displays text to STDOUT into one returning its output as a string:

# $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;
}
[download]

--Stevie-O

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

In reply to Re: The latest & greatest in 5.8.x? by Stevie-O
in thread The latest & greatest in 5.8.x? by drewbie

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