notes/strong-with-getonce.pl

   1 #!/usr/bin/env perl
   2
   3 use strict;
   4 use warnings;
   5 use Devel::GlobalDestruction ();
   6 use Scalar::Util ();
   7 use Variable::Magic ();
   8 use Carp ();
   9
  10 BEGIN {
  11   package Foo;
  12
  13   my $wiz;
  14   $wiz = Variable::Magic::wizard
  15     data => sub { $_[1] },
  16     get => sub {
  17       Carp::cluck "get fired";
  18       Variable::Magic::dispell ${$_[0]}, $wiz;
  19     };
  20
  21   sub DESTROY {
  22     return if Devel::GlobalDestruction::in_global_destruction();
  23     warn "DESTROY\n";
  24
  25     my $self = shift;
  26
  27     if (ref $self->{other_side} && $self->{other_side}{reference}) {
  28       if (
  29         Scalar::Util::refaddr($self->{other_side}{reference})
  30         eq Scalar::Util::refaddr($self)
  31       ) {
  32         warn "Enlivening";
  33         $self->{other_side}{reference} = $self;
  34         Variable::Magic::cast $self->{other_side}{reference}, $wiz;
  35         delete $self->{other_side};
  36       }
  37     }
  38   }
  39 }
  40
  41 my $near = {};
  42 my $far = $near->{reference} = bless({ other_side => $near }, 'Foo');
  43 warn $near->{reference};
  44 warn $far;
  45 Scalar::Util::weaken($near->{reference});
  46 warn "Setup done\n";
  47 undef($far);
  48 warn $near->{reference};
  49 warn $near->{reference};
  50 Scalar::Util::weaken($near->{reference});
  51 warn $near->{reference};