NullObject

Null Object

Purpose

NullObject is not a GoF design pattern but a schema which appears frequently enough to be considered a pattern. It has the following benefits:

• Client code is simplified
• Reduces the chance of null pointer exceptions
• Fewer conditionals require less test cases

Methods that return an object or null should instead return an object or NullObject. NullObjects simplify boilerplate code such as if (!is_null($obj)) { $obj->callSomething(); } to just $obj->callSomething(); by eliminating the conditional check in client code.

Examples

• Symfony2: null logger of profiler
• Symfony2: null output in Symfony/Console
• null handler in a Chain of Responsibilities pattern
• null command in a Command pattern

UML Diagram

Code

You can also find this code on GitHub

Service.php

.. literalinclude:: Service.php
   :language: php
   :linenos:

LoggerInterface.php

.. literalinclude:: LoggerInterface.php
   :language: php
   :linenos:

PrintLogger.php

.. literalinclude:: PrintLogger.php
   :language: php
   :linenos:

NullLogger.php

.. literalinclude:: NullLogger.php
   :language: php
   :linenos:

Test

Tests/LoggerTest.php

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