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Structural/DependencyInjection/index.rst

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+Dependency Injection
+====================
+
+Purpose
+-------
+
+To implement a loosely coupled architecture in order to get better
+testable, maintainable and extendable code.
+
+Usage
+-----
+
+Configuration gets injected and ``Connection`` will get all that it
+needs from ``$config``. Without DI, the configuration would be created
+directly in ``Connection``, which is not very good for testing and
+extending ``Connection``.
+
+Notice we are following Inversion of control principle in ``Connection``
+by asking ``$config`` to implement ``Parameters`` interface. This
+decouples our components. We don't care where the source of information
+comes from, we only care that ``$config`` has certain methods to
+retrieve that information. Read more about Inversion of control
+`here <http://en.wikipedia.org/wiki/Inversion_of_control>`__.
+
+Examples
+--------
+
+-  The Doctrine2 ORM uses dependency injection e.g. for configuration
+   that is injected into a ``Connection`` object. For testing purposes,
+   one can easily create a mock object of the configuration and inject
+   that into the ``Connection`` object
+-  Symfony and Zend Framework 2 already have containers for DI that
+   create objects via a configuration array and inject them where needed
+   (i.e. in Controllers)
+
+UML Diagram
+-----------
+
+.. image:: uml/uml.png
+   :alt: Alt DependencyInjection UML Diagram
+   :align: center
+
+Code
+----
+
+You can also find these code on `GitHub`_
+
+Connection.php
+
+.. literalinclude:: Connection.php
+   :language: php
+   :linenos:
+
+ArrayConfig.php
+
+.. literalinclude:: ArrayConfig.php
+   :language: php
+   :linenos:
+
+AbstractConfig.php
+
+.. literalinclude:: AbstractConfig.php
+   :language: php
+   :linenos:
+
+Parameters.php
+
+.. literalinclude:: Parameters.php
+   :language: php
+   :linenos:
+
+Test
+----
+
+Tests/DependencyInjectionTest.php
+
+.. literalinclude:: Tests/DependencyInjectionTest.php
+   :language: php
+   :linenos:
+
+Tests/config.php
+
+.. literalinclude:: Tests/config.php
+   :language: php
+   :linenos:
+
+.. _`GitHub`: https://github.com/domnikl/DesignPatternsPHP/tree/master/Structural/DependencyInjection