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
• Yii Framework: CFilterChain is a chain of controller action filters. the executing point is passed from one filter to the next along the chain, and only if all filters say "yes", the action can be invoked at last.

You can also find this code on GitHub

Handler.php

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

Responsible/SlowStorage.php

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

Responsible/FastStorage.php

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

Tests/ChainTest.php

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