Beam::Emitter - Role for event emitting classes
version 1.000
package My::Emitter;
use Moo;
with 'Beam::Emitter';
sub do_something {
my ( $self ) = @_;
# Give event listeners a chance to prevent something
my $event = $self->emit( "before_something" );
return if $event->is_default_stopped;
# ... do something
# Notify listeners we're done with something
$self->emit( 'after_something' );
}
sub custom_something {
my ( $self ) = @_;
# Send arbitrary arguments to our event listener
$self->emit_args( 'custom_something', "foo", "bar" );
}
This role is used by classes that want to emit events to subscribers. A subscriber registers interest in an event using the subscribe or on methods. Then, the class can emit events to be handled by any listening subscribers.
Using the Beam::Event class, subscribers can stop an event from being processed, or prevent the default action from happening.
Beam::Event is an event object with some simple methods to allow subscribers to influence the handling of the event. By calling the stop method, subscribers can stop all futher handling of the event. By calling the the stop_default method, subscribers can allow other subscribers to be notified about the event, but let the emitter know that it shouldn't continue with what it was going to do.
For example, let's build a door that notifies when someone tries to open it. Different instances of a door should allow different checks before the door opens, so we'll emit an event before we decide to open.
package Door;
use Moo;
with 'Beam::Emitter';
sub open {
my ( $self, $who ) = @_;
my $event = $self->emit( 'before_open' );
return if $event->is_default_stopped;
$self->open_the_door;
}
package main;
my $door = Door->new;
$door->open;
Currently, our door will open for anybody. But let's build a door that only open opens after noon (to keep us from having to wake up in the morning).
use Time::Piece;
my $restful_door = Door->new;
$restful_door->on( before_open => sub {
my ( $event ) = @_;
my $time = Time::Piece->now;
if ( $time->hour < 12 ) {
$event->stop_default;
}
} );
$restful_door->open;
By calling stop_default, we set the is_default_stopped flag, which the door sees and decides not to open.
The default Beam::Event
is really only useful for notifications. If you want
to give your subscribers some data, you need to create a custom event class.
This allows you to add attributes and methods to your events (with all
the type constraints and coersions you want).
Let's build a door that can keep certain people out. Right now, our door doesn't care who is trying to open it, and our subscribers do not get enough information to deny entry to certain people.
So first we need to build an event object that can let our subscribers know who is knocking on the door.
package Door::Knock;
use Moo;
extends 'Beam::Event';
has who => (
is => 'ro',
required => 1,
);
Now that we can represent who is knocking, let's notify our subscribers.
package Door;
use Moo;
use Door::Knock; # Our emitter must load the class, Beam::Emitter will not
with 'Beam::Emitter';
sub open {
my ( $self, $who ) = @_;
my $event = $self->emit( 'before_open', class => 'Door::Knock', who => $who );
return if $event->is_default_stopped;
$self->open_the_door;
}
Finally, let's build a listener that knows who is allowed in the door.
my $private_door = Door->new;
$private_door->on( before_open => sub {
my ( $event ) = @_;
if ( $event->who ne 'preaction' ) {
$event->stop_default;
}
} );
$private_door->open;
Although checking is_default_stopped
is completely optional, if you do not
wish to use the Beam::Event
object, you can instead call emit_args
instead of emit to give arbitrary arguments to your listeners.
package Door;
use Moo;
with 'Beam::Emitter';
sub open {
my ( $self, $who ) = @_;
$self->emit_args( 'open', $who );
$self->open_the_door;
}
There's no way to stop the door being opened, but you can at least notify someone before it does.
Subscribe to an event from this object. event_name
is the name of the event.
subref
is a subroutine reference that will get either a Beam::Event object
(if using the emit method) or something else (if using the emit_args method).
Alias for "subscribe".
Unsubscribe from an event. event_name
is the name of the event. subref
is
the single listener subref to be removed. If no subref is given, will remove
all listeners for this event.
An alias for "unsubscribe"
Emit a Beam::Event with the given name
. event_args
is a list of name => value
pairs to give to the Beam::Event
constructor.
Use the class
key in event_args
to specify a different Event class.
Emit an event with the given name
. callback_args
is a list that will be given
directly to each subscribed callback.
Use this if you want to avoid using Beam::Event, though you miss out on the control features like stop and stop default.
-
http://perladvent.org/2013/2013-12-16.html
Coordinating Christmas Dinner with Beam::Emitter by Yanick Champoux.
Doug Bell preaction@cpan.org
Joel Berger joel.a.berger@gmail.com
This software is copyright (c) 2015 by Doug Bell.
This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.