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The Hoa\Event library
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Hoa is a modular, extensible and structured set of PHP libraries.
Moreover, Hoa aims at being a bridge between industrial and research worlds.


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This library allows to use events and listeners in PHP. This is an observer design-pattern implementation.

Learn more.


With Composer, to include this library into your dependencies, you need to require hoa/event:

$ composer require hoa/event '~2.0'

For more installation procedures, please read the Source page.


Before running the test suites, the development dependencies must be installed:

$ composer install

Then, to run all the test suites:

$ vendor/bin/hoa test:run

For more information, please read the contributor guide.

Quick usage

We propose a quick overview of how to use events and listeners.


An event is:

  • Asynchronous when registering, because the observable may not exist yet while observers start to observe,
  • Anonymous when using, because the observable has no idea how many and what observers are observing,
  • It aims at a large diffusion of data through isolated components. Wherever is the observable, we can observe its data.

In Hoa, an event channel has the following form: hoa://Event/LibraryName/AnId:pseudo-class#anAnchor. For instance, the hoa://Event/Exception channel contains all exceptions that have been thrown. The hoa://Event/Stream/StreamName:close-before contains all streams that are about to close. Thus, the following example will observe all thrown exceptions:

    function (Hoa\Event\Bucket $bucket) {

Because attach expects a callable and because Hoa's callable implementation is smart, we can directly attach a stream to an event, like:

    new Hoa\File\Write('Foo.log')

This way, all exceptions will be printed on the Foo.log file.


Contrary to an event, a listener is:

  • Synchronous when registering, because the observable must exist before observers can observe,
  • Identified when using, because the observable knows how many observers are observing,
  • It aims at a close diffusion of data. The observers must have an access to the observable to observe.

The Hoa\Event\Listenable interface requires the on method to be present to register a listener to a listener ID. For instance, the following example listens the message listener ID, i.e. when a message is received by the WebSocket server, the closure is executed:

$server = new Hoa\Websocket\Server(…);
$server->on('message', function (Hoa\Event\Bucket $bucket) {


The hack book of Hoa\Event contains detailed information about how to use this library and how it works.

To generate the documentation locally, execute the following commands:

$ composer require --dev hoa/devtools
$ vendor/bin/hoa devtools:documentation --open

More documentation can be found on the project's website:

Getting help

There are mainly two ways to get help:


Do you want to contribute? Thanks! A detailed contributor guide explains everything you need to know.


Hoa is under the New BSD License (BSD-3-Clause). Please, see LICENSE for details.

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