To build a chain of objects to handle a call in sequential order. If one object cannot handle a call, it delegates the call to the next in the chain and so forth.

• logging framework, where each chain element decides autonomously what to do with a log message
• a Spam filter
• Caching: first object is an instance of e.g. a Memcached Interface, if that "misses" it delegates the call to the database interface

You can also find this code on GitHub

Handler.php

.. literalinclude:: Handler.php
   :language: php
   :linenos:

Responsible/FastStorage.php

.. literalinclude:: Responsible/HttpInMemoryCacheHandler.php
   :language: php
   :linenos:

Responsible/SlowStorage.php

.. literalinclude:: Responsible/SlowDatabaseHandler.php
   :language: php
   :linenos:

Tests/ChainTest.php

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