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Evented-Object-5.63
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NAME

Evented::Object - a 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.

Glossary

These terms are used throughout the Evented::Object documentation.

This base class, providing methods for managing events.

Refers to any object instance of Evented::Object or a package which inherits
from it.

See ["Evented object methods"](#evented-object-methods).

Event responders, known as callbacks, consist of a code reference and sometimes
additional options describing how and when they should be executed.

They are executed in descending order by priority. Numerically larger priorities
are called first. This allows you to place a certain callback in front of or
behind another.

An object representing an event fire.

The fire object provides methods for fetching information related to the current
event fire. It also provides an interface for modifying the behavior of the
remaining callbacks.

Fire objects are specific to the particular event fire, not the event. If you
fire the same event twice in a row, the event object used the first time will
not be the same as the second time. Therefore, all modifications made by the
fire object's methods apply only to the callbacks remaining in this particular
fire. For example, `$fire->cancel($callback)` will only cancel the supplied
callback once.

See ["Fire object methods"](#fire-object-methods).

An object representing a group of callbacks waiting to be fired.

Sometimes it is useful to prepare an event fire before actually calling it.
This way, you can provide special options for the fire. Collections are returned
by the 'prepare' methods.

    $eo->prepare(event_name => @args)->fire(some_fire_option => $value);

See ["Collection methods"](#collection-methods).

An evented object that receives event notifications from another evented object.

Additional evented objects can be registered as "listeners," which allows them
to respond to the events of another evented object.

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 mooing is
`cow.moo`.

**Fire objects and listeners**

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:

- **$fire->event\_name**: the name of the event from the perspective of the
listener; i.e. `cow.moo` (NOT `moo`)
- **$fire->object**: the 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, including those belonging to the evented object.

Evented::Object's included core packages are prefixed with Evented::Object::. Other packages which are specifically designed for use with Evented::Object are prefixed with Evented::.

Evented object methods

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

%options - event handler options

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

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 events 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

$eo->delete_event($event_name)

Deletes all callbacks registered for the supplied event.

Returns a true value if any events were deleted, false otherwise.

$eo->delete_event('myEvent');

Parameters

$eo->delete_callback($event_name)

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

Returns a true value if any events were deleted, false otherwise.

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

Parameters

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

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

$eo->fire_event('some_event');

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

Parameters

$eo->fire_once($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.

$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

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

Makes the passed evented object a listener of this evented object. See the "listener objects" section for more information on this feature.

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

Parameters

$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".

$eo->delete_listener($other_eo)

Removes a listener of this evented object. See the "listener objects" section for more information on this feature.

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

Parameters

$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.

Preparation methods

Callbacks can be prepared before being fired. This is most useful for firing events with special fire options.

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

Prepares a single event for firing. Returns a collection object representing the callbacks for the event.

# 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.

$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 ]
);

Class monitors

$eo->monitor_events($pkg)

Registers an evented object as the class monitor for a specific package. See the section above for more details on class monitors and their purpose.

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

$eo->stop_monitoring($pkg)

Removes an evented object from its current position as a monitor for a specific package. See the section above for more details on class monitors and their purpose.

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

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 entire routine. 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
);

Parameters

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

Collection methods

"Collections" are returned by the 'prepare' methods. They represent a group of callbacks that are about to be fired.

$col->fire(@options)

Fires the pending callbacks with the specified options, if any. If the callbacks have not yet been sorted, they are sorted before the event is fired.

$eo->prepare(some_event => @arguments)->fire('safe');

Parameters

@options

$col->sort

Sorts the callbacks according to priority, before, and after options.

Fire object methods

"Fire objects" are passed to all callbacks of an Evented::Object (unless the silent parameter was specified.) Fire objects contain information about the event itself, the callback, the caller of the event, event data, and more.

$fire->object

Returns the evented object.

$fire->object->delete_event('myEvent');

$fire->caller

Returns the value of caller(1) from within the ->fire() method. This allows you to determine from where the event was fired.

my $name   = $fire->event_name;
my @caller = $fire->caller;
say "Package $caller[0] line $caller[2] called event $name";

$fire->stop($reason)

Cancels all remaining callbacks. This stops the rest of the event firing. After a callback calls $fire->stop, the name of that callback is stored as $fire->stopper.

If the event has already been stopped, this method returns the reason for which the fire was stopped or "unspecified" if no reason was given.

# ignore messages from trolls
if ($user eq 'noah') {
    # user is a troll.
    # stop further callbacks.
    return $fire->stop;
}

$fire->stopper

Returns the callback which called $fire->stop.

if ($fire->stopper) {
    say 'Fire was stopped by '.$fire->stopper;
}

$fire->exception

If the event was fired with the safe option, it is possible that an exception occurred in one (or more if fail_continue enabled) callbacks. This method returns the last exception that occurred or undef if none did.

if (my $e = $fire->exception) {
   say "Exception! $e";
}

$fire->called($callback)

If no argument is supplied, returns the number of callbacks called so far, including the current one. If a callback argument is supplied, returns whether that particular callback has been called.

say $fire->called, 'callbacks have been called so far.';

if ($fire->called('some.callback')) {
    say 'some.callback has been called already.';
}

Parameters

$fire->pending($callback)

If no argument is supplied, returns the number of callbacks pending to be called, excluding the current one. If a callback argument is supplied, returns whether that particular callback is pending for being called.

say $fire->pending, ' callbacks are left.';

if ($fire->pending('some.callback')) {
    say 'some.callback will be called soon (unless it gets canceled)';
}

Parameters

$fire->cancel($callback)

Cancels the supplied callback once.

if ($user eq 'noah') {
    # we don't love noah!
    $fire->cancel('send.hearts');
}

Parameters

$fire->return_of($callback)

Returns the return value of the supplied callback.

if ($fire->return_of('my.callback')) {
    say 'my.callback returned a true value';
}

Parameters

$fire->last

Returns the most recent previous callback called. This is also useful for determining which callback was the last to be called.

say $fire->last, ' was called before this one.';

my $fire = $eo->fire_event('myEvent');
say $fire->last, ' was the last callback called.';

$fire->last_return

Returns the last callback's return value.

if ($fire->last_return) {
    say 'the callback before this one returned a true value.';
}
else {
    die 'the last callback returned a false value.';
}

$fire->event_name

Returns the name of the event.

say 'the event being fired is ', $fire->event_name;

$fire->callback_name

Returns the name of the current callback.

say 'the current callback being called is ', $fire->callback_name;

$fire->callback_priority

Returns the priority of the current callback.

say 'the priority of the current callback is ', $fire->callback_priority;

$fire->callback_data($key)

Returns the data supplied to the callback when it was registered, if any. If the data is a hash reference, an optional key parameter can specify a which value to fetch.

say 'my data is ', $fire->callback_data;
say 'my name is ', $fire->callback_data('name');

Parameters

$fire->data($key)

Returns the data supplied to the collection when it was fired, if any. If the data is a hash reference, an optional key parameter can specify a which value to fetch.

say 'fire data is ', $fire->data;
say 'fire time was ', $fire->data('time');

Parameters

Aliases

A number of aliases exist for convenience, but some of the names are rather broad. For that reason, they are only recommended for use when you are sure 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.

ADVANCED FEATURES

Registering callbacks to package names

The methods ->register_callback(), ->delete_event(), ->delete_callback, etc. can be called in the form of MyClass->method(). Evented::Object will store these callbacks in the package's symbol table.

Any object of this class will borrow these callbacks from the class. They will be incorporated into the callback collection as though they were registered directly on the object.

Note that events cannot be fired on a class, only on evented objects.

Note that if an evented object is blessed to a subclass of a class with callbacks registered to it, the object will NOT inherit the callbacks associated with the parent class. Callbacks registered to classes ONLY apply to objects directly blessed to the class.

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.

AUTHOR

Mitchell Cooper cooper@cpan.org

Copyright © 2011-2017. Released under BSD license.

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