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    Object::Event - A class that provides an event callback interface

    Version 0.6

       package foo;
       use Object::Event;

       our @ISA = qw/Object::Event/;

       package main;
       my $o = foo->new;

       my $regid = $o->reg_cb (foo => sub {
          print "I got an event, with these args: $_[1], $_[2], $_[3]\n";

       $o->event (foo => 1, 2, 3);

       $o->unreg_cb ($regid);

    This module was mainly written for Net::XMPP2, Net::IRC3,
    AnyEvent::HTTPD and BS to provide a consistent API for registering and
    emitting events. Even though I originally wrote it for those modules I
    relased it seperately in case anyone may find this module useful.

    For more comprehensive event handling see also Glib and POE.

    This class provides a simple way to extend a class, by inheriting from
    this class, with an event callback interface.

    You will be able to register callbacks for event names and call them

    In the first version as presented here no special performance
    optimisations have been applied. So take care that it is fast enough for
    your purposes. At least for modules like Net::XMPP2 the overhead is
    probably not noticeable, as other technologies like XML already waste a
    lot more CPU cycles.

    new (%hashcontent)
        This is a convenience constructor. It will create a blessed
        hashreference initialized with %hashcontent.

    set_exception_cb ($cb)
        This method installs a callback that will be called when some other
        event callback threw an exception. The first argument to $cb will be
        the exception.

    reg_cb ($eventname1, $cb1, [$eventname2, $cb2, ...])
        This method registers a callback $cb1 for the event with the name
        $eventname1. You can also pass multiple of these eventname =>
        callback pairs.

        The return value will be an ID that represents the set of callbacks
        you have installed. Call "unreg_cb" with that ID to remove those
        callbacks again.

        The callbacks will be called in an array context. If a callback
        doesn't want to return any value it should return an empty list. All
        results from the callbacks will be appended and returned by the
        "event" method.

        For every event there will also be two other event callbacks called:

        Before the callbacks for $eventname is being exectued the callback
        for "before_$eventname" is being called. And after the callbacks for
        $eventname have been run, the callback "after_$eventname" is being

        The "before_$eventname" callbacks allow you to stop the execution of
        all callbacks for the event $eventname and "after_$eventname". This
        can be used to intercept events and stop them.

        If you give reg_cb a special argument called "_while_referenced" you
        can prevent callbacks from being executed once the reference in the
        second argument becomes undef. This works by converting the internal
        reference of the argument to "_while_referenced" to a weak reference
        and looking whether that reference becomes undef.

        It works like this:

           Scalar::Util::weaken $window;
           $event_source->reg_cb (
              _while_referenced => $window,
              disconnect => sub { $window->destroy }

        Whenever the "disconnect" event is emitted now and $window doesn't
        exist anymore the callback will be removed.

    unreg_cb ($id)
        Removes the set $id of registered callbacks. $id is the return value
        of a "reg_cb" call.

    event ($eventname, @args)
        Emits the event $eventname and passes the arguments @args. The
        return value is a list of defined return values from the event

        See also the specification of the before and after events in
        "reg_cb" above.

        NOTE: Whenever an event is emitted the current set of callbacks
        registered to that event will be used. So, if you register another
        event callback for the same event that is executed at the moment, it
        will be called the next time when the event is emitted. Example:

           $obj->reg_cb (event_test => sub {
              my ($obj) = @_;

              print "Test1\n";

              $obj->reg_cb (event_test => sub {
                 print "Test2\n";

           $obj->event ('event_test'); # prints "Test1"
           $obj->event ('event_test'); # prints "Test2"

    _event ($eventname, @args)
        This directly executes the event $eventname without executing
        callbacks of the before and after events (as specified in "reg_cb"

        If this method is called from a callback on the first argument to
        the callback (i.e. $self) the callback will be deleted after it is

        When called in a 'before_' event callback then the execution of the
        event is stopped after all 'before_' callbacks have been run.

        When callend in the main event callback, the event is stopped after
        all the main event callbacks have been run.

    add_forward ($obj, $forward_cb)
        This method allows to forward all events to an object. $forward_cb
        will be called everytime an event is generated in $self. The first
        argument to the callback $forward_cb will be $self, the second will
        be $obj, the third will be the event name and the rest will be the
        event arguments. (For third and rest of argument also see
        description of "event").

        (Please note that it might be most useful to call "_event" in the
        callback to allow objects that receive the forwarded events to react

    remove_forward ($obj)
        This method removes a forward. $obj must be the same object that was
        given "add_forward" as the $obj argument.

        This method removes all registered event callbacks and forwards from
        this object.

        This method returns a string dump of all registered event callbacks.
        This method is only for debugging purposes.

    Robin Redeker, "<elmex at>", JID: "<elmex at>"

    Copyright 2007 Robin Redeker, all rights reserved.

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