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1 non-PAUSE user
Author image Salvador Fandiño García


Method::WeakCallback - Call back object methods through weak references.


  package Foo::Bar;
  use Method::WeakCallback qw(weak_method_callback);

  use AE;

  sub new { ... }

  sub set_timer {
    my $obj = shift;
    $obj->{timer} = AE::timer(60, 60,
                        weak_method_callback($obj, 'on_timeout'));

  sub on_timeout { say "Time out!" }


When writing programs mixing event programming with OOP, it is very common to employ callbacks that just call some method on some object. I.e.:

  $w = AE::io($fh, 0, sub { $obj->data_available_for_reading });

Unfortunately, this style can result in the creation of cyclic data structures that never get freed.

For instance consider the following code:

  $obj->{rw} = AE::io($fh, 0, sub { $obj->data_available_for_reading });

The callback is a closure that internally, keeps a reference to $obj. Then a reference to the callback is stored in the watcher object which is itself stored in $obj and so, the cycle is complete.

Method::WeakCallback solves that problem generating callbacks that use a weak reference for the object. Its usage is very simple:

  $obj->{rw} = AE::io($fh, 0,
                    weak_method_callback($obj, 'data_available_for_reading'));

If the callback is called after $obj is destroyed it will just do nothing.

Extra arguments to be passed to the method can also be given. I.e.

  weak_method_callback($obj, $method, @extra);

  # equivalent to:
  #   sub { $obj->$method(@extra, @_) };

The module also provides the subroutine weak_method_callback_cached which stores inside an internal cache the generated callbacks greatly improving performance when the same callback (same object, same method) is generated over and over.

Note that weak_method_callback_cached does not accept extra arguments.


None by default.

The subroutines weak_method_callback and weak_method_callback_cached can be imported from this module.


curry, AnyEvent.


Salvador Fandiño, <sfandino@yahoo.com>


Copyright (C) 2013 by Qindel Formación y Servicios S.L.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.14.2 or, at your option, any later version of Perl 5 you may have available.