package Value::Canary;
our $VERSION = '0.01';

# ABSTRACT: Callbacks for value destruction

use Carp 'cluck';
use Variable::Magic qw/wizard cast/;
use namespace::clean;

use Sub::Exporter -setup => {
    exports => ['canary'],
    groups  => { default => ['canary'] },

my $wiz = wizard data => sub { $_[1] },
                 free => sub { $_[1]->($_[0]) };

sub canary {
    my $cb = $_[1];
    $cb ||= sub { cluck "${ $_[0] } destroyed" };
    cast $_[0], $wiz, $cb;



=head1 NAME

Value::Canary - Callbacks for value destruction

=head1 VERSION

version 0.01


    use Value::Canary;

    my $i = 0;

        my $value = 42;
        canary $value, sub { $i++ };


        # $i is still 0
    } # end of scope causes $value to be destroyed and the callback to be invoked

    # $i is now 1


This module provides an easy way to get notified as soon as a value is being
destroyed. This is mostly handy for debugging purposes, when you want to find
out which code is throwing the value you passed in away, instead of using it
for something useful.


=head2 canary ($variable, $callback?)

Registers a C<$callback> to be called as soon as C<$variable> is being
destroyed. The callback will be invoked with a reverence to the C<$variable> as
its only argument. If no callback is given, a default callback will be used.
The default callback will warn with a full stack trace of where the value is
being destroyed, as well as the message C<"$value destroyed">.

This function is exported by default. See L<Sub::Exporter> on how to customize
how exactly exporting happens.

=head1 SEE ALSO




=head1 AUTHOR

  Florian Ragwitz <>


This software is copyright (c) 2009 by Florian Ragwitz.

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.