# phpman > man > POE::Component(3pm)

## NAME
    [POE::Component](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AComponent/markdown) - event driven objects or subsystems

## SYNOPSIS
    See specific components.

## DESCRIPTION
    POE "components" are event-driven modules that generally encapsulate mid- to high-level program
    features. For example, [POE::Component::Client::DNS](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AComponent%3A%3AClient%3A%3ADNS/markdown) performs message-based asynchronous resolver
    lookups. [POE::Component::Server::TCP](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AComponent%3A%3AServer%3A%3ATCP/markdown) is a basic asynchronous network server.

    The [POE::Component](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AComponent/markdown) namespace was started as place for contributors to publish their POE-based
    modules without requiring coordination with the main POE distribution. The namespace predates
    the -X convention, otherwise you'd be reading about POEx instead.

    As with many things in Perl, there is more than one way to implement component interfaces. Newer
    components sport OO interfaces, and some even use Moose, but older ones are solely message
    driven.

## OBJECT ORIENTED COMPONENTS
    One way to create object-oriented components is to embed a [POE::Session](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3ASession/markdown) instance within an
    object. This is done by creating the session during the object's constructor, setting the
    session's alias to something unique, and saving a copy of the alias in the object.

      package Asynchrotron;

      my $alias_index = 0;

      sub new {
        my $class = shift;
        my $self = bless {
          alias => __PACKAGE__ . " " . ++$alias_index;
        }, $class;

        [POE::Session](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3ASession/markdown)->create(
          object_states => [
            $self => {
              _start       => "_poe_start",
              do_something => "_poe_do_something",
            },
          ],
        );
        return $self;
      }

      sub _poe_start {
        $_[KERNEL]->alias_set($_[OBJECT]->{alias});
      }

    The alias allows object methods to pass events into the session without having to store
    something about the session. The [POE::Kernel](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AKernel/markdown) call() transfers execution from the caller
    session's context into the component's session.

      sub do_something {
        my $self = shift;
        print "Inside the caller's session right now: @_\n";
        $poe_kernel->call($self->{alias}, "do_something", @_);
      }

      sub _poe_do_something {
        my @args = @_[ARG0..$#_];
        print "Inside the component's session now: @args\n";
        $_[OBJECT]{count}++;
      }

    Both $_[HEAP] and $_[OBJECT] are visible within the component's session. $_[HEAP] can be used
    for ultra-private encapsulation, while $_[OBJECT] may be used for data visible by accessors.

      sub get_count {
        my $self = shift;
        return $self->{count}; # $_[OBJECT]{count} above
      }

    Too many sessions may bog down object creation and destruction, so avoid creating them for every
    object.

## SEE ALSO
    The SEE ALSO section in POE contains a table of contents covering the entire POE distribution.

    [POE::Stage](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AStage/markdown) is a nascent project to formalize POE components, make [POE::Kernel](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AKernel/markdown) more
    object-oriented, and provide syntactic and semantic sugar for many common aspects of
    [POE::Component](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AComponent/markdown) development. It's also easier to type. Please investigate the project. Ideas and
    *tuits* are badly needed to help get the project off the ground.

## TO DO
    Document the customary (but not mandatory!) process of creating and publishing a component.

AUTHORS & COPYRIGHTS
    Each component is written and copyrighted separately.

    Please see POE for more information about authors and contributors.