NAME
Beam::Emitter - Role for event emitting classes
VERSION
version 0.007
SYNOPSIS
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" );
}
DESCRIPTION
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.
Using Beam::Event
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 stop_default, 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.
Using Custom Events
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;
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;
Without Beam::Event
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.
ATTRIBUTES
_listeners
The event listeners registered on this object.
METHODS
subscribe ( event_name, subref )
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).
on ( event_name, subref )
Alias for "subscribe".
unsubscribe ( event_name [, subref ] )
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.
un ( event_name [, subref ] )
An alias for "unsubscribe"
emit ( name, event_args )
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_args ( name, callback_args )
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.
SEE ALSO
Beam::Event
<http://perladvent.org/2013/2013-12-16.html>
Coordinating Christmas Dinner with Beam::Emitter by Yanick Champoux.
AUTHOR
Doug Bell <preaction@cpan.org>
COPYRIGHT AND LICENSE
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.