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. NullObject\ s simplify boilerplate code such as if (!is_null($obj)) { $obj->callSomething(); } to just $obj->callSomething(); by eliminating the conditional check in client code.

Examples

• Null logger or null output to preserve a standard way of interaction between objects, even if the shouldn't do anything
• null handler in a Chain of Responsibilities pattern
• null command in a Command pattern

UML Diagram

.. image:: uml/uml.png :alt: Alt NullObject UML Diagram :align: center

Code

You can also find this code on GitHub_

Service.php

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

Logger.php

.. literalinclude:: Logger.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:

.. _GitHub: https://github.com/DesignPatternsPHP/DesignPatternsPHP/tree/main/Behavioral/NullObject .. __: http://en.wikipedia.org/wiki/Null_Object_pattern