Mitchell Cooper

NAME

Evented::Object - base class which allows you to attach callbacks to objects and then fire events on them.

SYNOPSIS

 package Person;
 
 use warnings;
 use strict;
 use 5.010;
 use parent 'Evented::Object';
 
 use Evented::Object;
 
 # Creates a new person object. This is nothing special.
 # Evented::Object does not require any specific constructor to be called.
 sub new {
     my ($class, %opts) = @_;
     bless \%opts, $class;
 }
 
 # Fires birthday event and increments age.
 sub have_birthday {
     my $person = shift;
     $person->fire(birthday => ++$person->{age});
 }

In some other package...

 package main;
 
 # Create a person named Jake at age 19.
 my $jake = Person->new(name => 'Jake', age => 19);
 
 # Add an event callback that assumes Jake is under 21.
 $jake->on(birthday => sub {
     my ($fire, $new_age) = @_;
     say 'not quite 21 yet...';
 }, name => '21-soon');
 
 # Add an event callback that checks if Jake is 21
 # and cancels the above callback if so.
 $jake->on(birthday => sub {
  my ($fire, $new_age) =  @_;
     if ($new_age == 21) {
          say 'time to get drunk!';
          $fire->cancel('21-soon');
     }
 }, name => 'finally-21', priority => 1);
 
 # Jake has two birthdays.
 
 # Jake's 20th birthday.
 $jake->have_birthday;
 
 # Jake's 21st birthday.
 $jake->have_birthday;
 
 # Because 21-soon has a lower priority than finally-21,
 # finally-21 will cancel 21-soon if Jake is 21.
 
 # The result:
 #
 #   not quite 21 yet...
 #   time to get drunk!

DESCRIPTION

I doubt your objects have ever been this evented in your entire life.

Evented::Object supplies an (obviously objective) interface to store and manage callbacks for events, fire events upon objects, and more.

Evented::Object allows you to attach event callbacks to an object (i.e., a blessed hash reference) and then fire events on that object. Event fires are much like method calls, except that there can be many responders.

Whereas many event systems involve globally unique event names, Evented::Object allows you to attach events on specific objects. The event callbacks, priority options, and other data are stored within the object itself.

MANAGING CALLBACKS

The Evented::Object package provides several convenient methods for managing an event-driven object.

Evented::Object->new()

Creates a new Evented::Object.

Typically, this method is overriden by a child class of Evented::Object.

 my $eo = Evented::Object->new();

$eo->register_callback($event_name => \&callback, %options)

Attaches an event callback the object.

When the specified event is fired, each of the callbacks registered using this method will be called by descending priority order (numerically higher priority numbers are called first.)

 $eo->register_callback(myEvent => sub {
     ...
 }, name => 'some.callback', priority => 200);

Parameters

  • $event_name - name of the event.

  • \&callback - CODE reference to be called when the event is fired.

  • %options - optional, a hash (NOT a hash reference) of any of the below options.

%options - event handler options

All of these options are optional, but the use of a callback name is highly recommended.

  • name - name of the callback being registered. must be unique to this particular event.

  • priority - numerical priority of the callback.

  • before - name of a callback or an array reference of callback names to precede.

  • after - name of a callback or an array reference of callback names to succeed.

  • data - data that will be stored as $fire->callback_data as the callback is fired. If data is a hash reference, its values can be fetched conveniently with $fire->callback_data('key').

  • with_eo - if true, the evented object will prepended to the argument list (which is not the default behavior). note that this is enabled automatically when using the odd-argument version.

  • no_fire_obj - if true, the fire object will not be prepended to the argument list (which is the default behavior).

Note: the order of objects will always be $eo, $fire, @args, regardless of omissions. By default, the argument list is $fire, @args.

You may have any number of before and any number of after options for any given callback. For instance, one callback may specify to be before 'b' and 'c' but after 'a'. Evented::Object will resolve these priorities to its best ability.

In the case that the priorities can not be resolved (for instance, if a callback asks to be before 'a' and after 'b' while 'b' has already asked to be before 'a'), the behavior of Evented::Object is not guaranteed to be consistent. In other words, please do your best to not request impossible priorities.

In any case, before and after options are completely ignored when a priority is explicitly specified.

$eo->register_callback($event_name => \&callback, $cb_name, %options)

If the list of options is odd, it is assumed that the first element is the callback name. In this case, the with_eo option is also automatically enabled.

 $eo->register_callback(myEvent => sub {
     ...
 }, 'some.callback, priority => 200);

See the above method specification for parameters and supported options.

$eo->register_callbacks(@events)

Registers several event callbacks at once.

The arguments should be a list of hash references. These references take the same options as ->register_callback(). Returns a list of return values in the order that the events were specified.

 $eo->register_callbacks(
     { myEvent => \&my_event_1, name => 'cb.1', priority => 200 },
     { myEvent => \&my_event_2, name => 'cb.2', priority => 100 }
 );

Parameters

  • @events - array of hash references to pass to ->register_callback().

$eo->delete_event($event_name)

Deletes all callbacks registered for the supplied event.

Returns number of callbacks deleted, false if none.

 $eo->delete_event('myEvent');

Parameters

  • $event_name - name of the event.

$eo->delete_callback($event_name, $callback_name)

Deletes an event callback from the object with the given callback name.

Returns true if a callback was deleted.

 $eo->delete_callback(myEvent => 'my.callback');

Parameters

  • $event_name - name of the event.

  • $callback_name - name of the callback being removed.

$eo->delete_all_events()

Deletes all events and all callbacks from the object.

If you know that an evented object will no longer be used in your program, by calling this method you can be sure that no cyclical references from within callbacks will cause the object to be leaked.

FIRING EVENTS

$eo->fire_event($event_name => @arguments)

Fires the specified event, calling each callback that was registered with ->register_callback() in descending order of their priorities.

Returns the fire object.

 $eo->fire_event('some_event');

 $eo->fire_event(some_event => $some_argument, $some_other_argument);

Parameters

  • $event_name - name of the event being fired.

  • @arguments - optional, list of arguments to pass to event callbacks.

$eo->fire_once($event_name => @arguments)

Fires the specified event, calling each callback that was registered with ->register_callback() in descending order of their priorities.

Then, all callbacks for the event are deleted. This method is useful for situations where an event will never be fired more than once.

Returns the fire object.

 $eo->fire_once('some_event');
 $eo->fire_event(some_event => $some_argument, $some_other_argument);
 # the second does nothing because the first deleted the callbacks

Parameters

  • $event_name - name of the event being fired.

  • @arguments - optional, list of arguments to pass to event callbacks.

$eo->fire_events_together(@events)

The fire_events_together() function can be used as a method on evented objects. See the documentation for the function in "PROCEDURAL FUNCTIONS".

$eo->prepare_event(event_name => @arguments)

Prepares a single event for firing.

Returns an Evented::Object::Collection representing the pending callbacks.

 # an example using the fire option return_check.
 $eo->prepare_event(some_event => @arguments)->fire('return_check');

$eo->prepare_together(@events)

The preparatory method equivalent to ->fire_events_together.

Returns an Evented::Object::Collection representing the pending callbacks.

$eo->prepare(...)

A smart method that uses the best guess between ->prepare_event and ->prepare_together.

 # uses ->prepare_event()
 $eo->prepare(some_event => @arguments);

 # uses ->prepare_together()
 $eo->prepare(
    [ some_event => @arguments ],
    [ some_other => @other_arg ]
 );
 

LISTENERS

An evented object can listen for event notifications from another evented object using the method "$eo->add_listener($other_eo, $prefix)".

Consider a scenario where you have a class whose objects represent a farm. You have another class which represents a cow. You would like to use the same callback for all of the moos that occur on the farm, regardless of which cow initiated it.

Rather than attaching an event callback to every cow, you can instead make the farm a listener of the cow. Then, you can attach a single callback to your farm. If your cow's event for mooing is moo, your farm's event for any mooing is cow.moo.

When an event is fired on an object, the same fire object is used for callbacks belonging to both the evented object and its listening objects. Therefore, callback names should be unique not only to the listener object but to the object being listened on as well.

You should also note the values of the fire object:

  • $fire->event_name - name of the event from the perspective of the listener; i.e. cow.moo (NOT moo)

  • $fire->object - object being listened to; i.e. $cow (NOT $farm)

This also means that stopping the event from a listener object will cancel all remaining callbacks.

$eo->add_listener($other_eo, $prefix)

Makes the passed evented object a listener of this evented object.

See "LISTENERS".

 $cow->add_listener($farm, 'cow');

Parameters

  • $other_eo - evented object that will listen.

  • $prefix - string that event names will be prefixed with on the listener.

$eo->delete_listener($other_eo)

Removes a listener of this evented object.

See "LISTENERS".

 $cow->delete_listener($farm);

Parameters

  • $other_eo - evented object that will listen.

CLASS MONITORS

An evented object can be registered as a "monitor" of a specific class/package.

All event callbacks that are added from that class to any evented object of any type will trigger an event on the monitor object.

An example scenario of when this might be useful is an evented object for debugging all events being registered by a certain package. It would log all of them, making it easier to find a problem.

$eo->monitor_events($pkg)

Registers an evented object as the class monitor for a specific package.

See "CLASS MONITORS".

 my $some_eo  = Evented::Object->new;
 my $other_eo = Evented::Object->new;

 $some_eo->on('monitor:register_callback', sub {
     my ($event, $eo, $event_name, $cb) = @_;
     # $eo         == $other_eo
     # $event_name == "blah"
     # $cb         == callback hash from ->register_callback()
     say "Registered $$cb{name} to $eo for $event_name";
 });

 $some_eo->monitor_events('Some::Class');

 package Some::Class;
 $other_eo->on(blah => sub{}); # will trigger the callback above
  • $pkg - package whose event activity you wish to monitor.

$eo->stop_monitoring($pkg)

Removes an evented object from its current position as a monitor for a specific package.

See "CLASS MONITORS".

 $some_eo->stop_monitoring('Some::Class');
  • $pkg - package whose event activity you're monitoring.

PROCEDURAL FUNCTIONS

The Evented::Object package provides some functions for use. These functions typically are associated with more than one evented object or none at all.

fire_events_together(@events)

Fires multiple events at the same time.

This allows you to fire multiple similar events on several evented objects at the same time. It essentially pretends that the callbacks are all for the same event and all on the same object.

It follows priorities throughout all of the events and all of the objects, so it is ideal for firing similar or identical events on multiple objects.

The same fire object is used throughout. This means that callback names must unique among all of these objects and events. It also means that stopping an event from any callback will cancel all remaining callbacks, regardless to which event or which object they belong.

The function takes a list of array references in the form of: [ $evented_object, event_name => @arguments ]

 Evented::Object::fire_events_together(
     [ $server,  user_joined_channel => $user, $channel ],
     [ $channel, user_joined         => $user           ],
     [ $user,    joined_channel      => $channel        ]
 );

->fire_events_together can also be used as a method on any evented object.

 $eo->fire_events_together(
     [ some_event => @arguments ],
     [ some_other => @other_arg ]
 );

The above example would formerly be achieved as:

 Evented::Object::fire_events_together(
     [ $eo, some_event => @arguments ],
     [ $eo, some_other => @other_arg ]
 );

However, other evented objects may be specified even when this is used as a method. Basically, anywhere that an object is missing will fall back to the object on which the method was called.

 $eo->fire_events_together(
     [ $other_eo, some_event => @arguments ],
     [            some_other => @other_arg ] # no object, falls back to $eo
 );
 

Returns the fire object.

Parameters

  • @events - array of events in the form of [$eo, event_name => @arguments].

safe_fire($eo, $event_name, @args)

Safely fires an event. In other words, if the $eo is not an evented object or is not blessed at all, the call will be ignored. This eliminates the need to use blessed() and ->isa() on a value for testing whether it is an evented object.

 Evented::Object::safe_fire($eo, myEvent => 'my argument');

Parameters

  • $eo - evented object.

  • $event_name - name of the event.

  • @args - arguments for the event fire.

ALIASES

A number of aliases exist for convenience, but please only use them if you're certain that other subclassing will not interfere.

$eo->on(...)

Alias for $eo->register_callback().

$eo->del(...)

If one argument provided, alias for $eo->delete_event.

If two arguments provided, alias for $eo->delete_callback.

$eo->fire(...)

Alias for $eo->fire_event().

$eo->register_event(...)

Alias for $eo->register_callback().

$eo->register_events(...)

Alias for $eo->register_callbacks().

$fire->eo

Alias for $fire->object.

AUTHOR

Mitchell Cooper <cooper@cpan.org>

Copyright © 2011-2017. Released under New BSD license.

Comments, complaints, and recommendations are accepted. Bugs may be reported on GitHub.