Addon Capable Applications

[mattnoble]

I was just curious if anyone knew the general theory behind how to create PHP applications with addon support. How would you implement addons that people create and how exactly are they created. Are the addons just classes and functions that are added into the code somehow. I don't even know if I'm wording this right haha. What comes to mind mainly is WordPress, and it's huge addon repository and I was just curious if anyone knew how this was done, not specifically for WP, but in general. Thanks a lot!  :)

[Jenk]

Implement the Observer Pattern into the 'core' of your application (usually invoked by the front controller and stored in a registry.) Use strong interfaces, and provide plenty documentation.

Voila.. one plugin system.

EDIT: oh, and to implement the observer pattern is more than to just create a notify object, you'll actually need to have your application use it :)

[mattnoble]

That was fast haha. Thanks! Now, off to read some things  :)

[utexas_pjm]

The most straightforward way to implement a plugin system is to use php5 interfaces http://us3.php.net/interfaces.

Consider the following:

[code]
<?php
interface Foo
{
  public function getPluginName();
  public function mutateSomeObject(&$obj);
}
?>
[/code]

By using in an interface you are forcing plugins to implement certain methods, in this case getPluginName and mutateSomeObject.

A 3rd party plugin might look something like this:

[code]
<?php
class SomePlugin implements Foo
{
  public function getPluginName()
  {
    return 'MyPlugin';
  }

  public function mutateSomeObject(&$obj)
  {
    $obj->setProperty('foo');
  }
}
?>
[/code]

When you want to act on your plugin you might do something like this:

[code]
<?php
//..
$plugin =& PluginManager::getInstalledPlugin('SomePlugin');
echo 'Loading plugin ' . $plugin->getPluginName() . '...';
$plugin->mutateSomeObject($someObject);
?>
[/code]

Best,

Patrick

[mattnoble]

Cool, thank a lot Utexas! Hopefully I'll be able to get something going in the future. Appreciate it guys  :)

[Jenk]

Passing objects by reference raises E_STRICT errors, fyi.