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Facade

Purpose

The primary goal of a Facade Pattern is not to avoid you having to read the manual of a complex API. It's only a side-effect. The first goal is to reduce coupling and follow the Law of Demeter.

A Facade is meant to decouple a client and a sub-system by embedding many (but sometimes just one) interface, and of course to reduce complexity.

  • A facade does not forbid you the access to the sub-system
  • You can (you should) have multiple facades for one sub-system

That's why a good facade has no new in it. If there are multiple creations for each method, it is not a Facade, it's a Builder or a [Abstract|Static|Simple] Factory [Method].

The best facade has no new and a constructor with interface-type-hinted parameters. If you need creation of new instances, use a Factory as argument.

UML Diagram

Alt Facade UML Diagram

Code

You can also find this code on GitHub

Facade.php

.. literalinclude:: Facade.php
   :language: php
   :linenos:

OsInterface.php

.. literalinclude:: OsInterface.php
   :language: php
   :linenos:

BiosInterface.php

.. literalinclude:: BiosInterface.php
   :language: php
   :linenos:

Test

Tests/FacadeTest.php

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