This pattern provides an easy to decouple many components working together. It is a good alternative over Observer IF you have a "central intelligence", like a controller (but not in the sense of the MVC).

All components (called Colleague) are only coupled to the MediatorInterface and it is a good thing because in OOP, one good friend is better than many. This is the key-feature of this pattern.

You can also find these code on GitHub

MediatorInterface.php

.. literalinclude:: MediatorInterface.php
   :language: php
   :linenos:

Mediator.php

.. literalinclude:: Mediator.php
   :language: php
   :linenos:

Colleague.php

.. literalinclude:: Colleague.php
   :language: php
   :linenos:

Subsystem/Client.php

.. literalinclude:: Subsystem/Client.php
   :language: php
   :linenos:

Subsystem/Database.php

.. literalinclude:: Subsystem/Database.php
   :language: php
   :linenos:

Subsystem/Server.php

.. literalinclude:: Subsystem/Server.php
   :language: php
   :linenos:

Tests/MediatorTest.php

.. literalinclude:: Tests/MediatorTest.php
   :language: php
   :linenos: