dependency injection with php and php 5.3

Dependency Injection with PHP and PHP 5.3

Fabien Potencier

Fabien Potencier •  Serial entrepreneur and developer by passion •  Founder of Sensio (in 1998)

–  A services and consulting company specialized in Web technologies and Internet marketing (France and USA)

–  70 people –  Open-Source specialists –  Big corporate customers –  Consulting, training, development, web design, … and more –  Sponsor of a lot of Open-Source projects

like symfony and Doctrine

Fabien Potencier •  Creator and lead developer of symfony… •  and creator and lead developer of some more OSS:

–  symfony components –  Swift Mailer : Powerful component based mailing library for PHP –  Twig : Fexible, fast, and secure template language for PHP –  Pirum : Simple PEAR Channel Server Manager –  Sismo : PHP continuous integration server –  Lime : Easy to use unit testing library for PHP –  Twitto : A web framework in a tweet –  Twittee : A Dependency Injection Container in a tweet –  Pimple : A small PHP 5.3 dependency injection container

Fabien Potencier

•  Read my technical blog: http://fabien.potencier.org/

•  Follow me on Twitter: @fabpot

•  Fork my code on Github: http://github.com/fabpot/

Dependency Injection

A real world « web » example

In most web applications, you need to manage the user preferences

–  The user language – Whether the user is authenticated or not –  The user credentials – …

This can be done with a User object

–  setLanguage(), getLanguage() –  setAuthenticated(), isAuthenticated() –  addCredential(), hasCredential() –  ...

The User information need to be persisted

between HTTP requests

We use the PHP session for the Storage

class SessionStorage { function __construct($cookieName = 'PHP_SESS_ID') { session_name($cookieName); session_start(); }

function set($key, $value) { $_SESSION[$key] = $value; }

// ... }

class User { protected $storage;

function __construct() { $this->storage = new SessionStorage(); }

function setLanguage($language) { $this->storage->set('language', $language); }

// ... }

$user = new User();

Very easy to use

Very hard to

customize

class User { protected $storage;

function __construct($storage) { $this->storage = $storage; } }

$storage = new SessionStorage(); $user = new User($storage);

Slightly more

difficult to use

Very easy to

customize

That’s Dependency Injection

Nothing more

Let’s understand why the first example is not a good idea

I want to change the session cookie name

class User { protected $storage;

function __construct() { $this->storage = new SessionStorage('SESSION_ID'); }

function setLanguage($language) { $this->storage->set('language', $language); }

// ... }

$user = new User();

Hardcode it in the

User class

class User { protected $storage;

function __construct() { $this->storage = new SessionStorage(STORAGE_SESSION_NAME); } }

define('STORAGE_SESSION_NAME', 'SESSION_ID');

$user = new User();

Add a global

configuration?

class User { protected $storage;

function __construct($sessionName) { $this->storage = new SessionStorage($sessionName); } }

$user = new User('SESSION_ID');

Configure via

User?

class User { protected $storage;

function __construct($storageOptions) { $this->storage = new SessionStorage($storageOptions['session_name']);

$user = new User( array('session_name' => 'SESSION_ID') );

Configure with an

array?

I want to change the session storage implementation

Filesystem MySQL

Memcached …

class User { protected $storage;

function __construct() { $this->storage = Registry::get('session_storage'); } }

$storage = new SessionStorage(); Registry::set('session_storage', $storage); $user = new User();

Use a global

registry object?

Now, the User depends on the Registry

Instead of harcoding the Storage dependency

inside the User class constructor

Inject the Storage dependency in the User object

class User { protected $storage;

function __construct($storage) { $this->storage = $storage; } }

$storage = new SessionStorage('SESSION_ID'); $user = new User($storage);

What are the advantages?

Use different Storage strategies

class User { protected $storage;

function __construct($storage) { $this->storage = $storage; } }

$storage = new MySQLSessionStorage('SESSION_ID'); $user = new User($storage);

Use a different

Storage engine

Configuration becomes natural

class User { protected $storage;

function __construct($storage) { $this->storage = $storage; } }

$storage = new MySQLSessionStorage('SESSION_ID'); $user = new User($storage);

Configuration

is natural

Wrap third-party classes (Interface / Adapter)

class User { protected $storage;

function __construct(SessionStorageInterface $storage) { $this->storage = $storage; } }

interface SessionStorageInterface { function get($key);

function set($key, $value); }

Add an interface

Mock the Storage object (for testing)

class User { protected $storage;

function __construct(SessionStorageInterface $storage) { $this->storage = $storage; } }

class SessionStorageForTests implements SessionStorageInterface { protected $data = array();

static function set($key, $value) { self::$data[$key] = $value; } }

Mock the Session

Use different Storage strategies

Configuration becomes natural

Wrap third-party classes (Interface / Adapter)

Mock the Storage object (for testing)

Easy without changing the User class

« Dependency Injection is where components are given their dependencies

through their constructors, methods, or directly into fields. »

http://www.picocontainer.org/injection.html

$storage = new SessionStorage();

// constructor injection $user = new User($storage);

// setter injection $user = new User(); $user->setStorage($storage);

// property injection $user = new User(); $user->storage = $storage;

A slightly more complex web example

$request = new Request(); $response = new Response();

$storage = new FileSessionStorage('SESSION_ID'); $user = new User($storage);

$cache = new FileCache( array('dir' => dirname(__FILE__).'/cache') ); $routing = new Routing($cache);

class Application { function __construct() { $this->request = new WebRequest(); $this->response = new WebResponse();

$storage = new FileSessionStorage('SESSION_ID'); $this->user = new User($storage);

$cache = new FileCache( array('dir' => dirname(__FILE__).'/cache') ); $this->routing = new Routing($cache); } }

$application = new Application();

Back to square 1

class Application { function __construct() { $this->request = new WebRequest(); $this->response = new WebResponse();

$storage = new FileSessionStorage('SESSION_ID'); $this->user = new User($storage);

$cache = new FileCache( array('dir' => dirname(__FILE__).'/cache') ); $this->routing = new Routing($cache); } }

$application = new Application();

We need a Container

Describes objects and their dependencies

Instantiates and configures objects on-demand

A container SHOULD be able to manage

any PHP object (POPO)

The objects MUST not know that they are managed

by a container

•  Parameters –  The SessionStorageInterface implementation we want to use (the class name) –  The session name

•  Objects –  SessionStorage –  User

•  Dependencies –  User depends on a SessionStorageInterface implementation

Let’s build a simple container with PHP 5.3

DI Container

Managing parameters

class Container { protected $parameters = array();

public function setParameter($key, $value) { $this->parameters[$key] = $value; }

public function getParameter($key) { return $this->parameters[$key]; } }

$container = new Container(); $container->setParameter('session_name', 'SESSION_ID'); $container->setParameter('storage_class', 'SessionStorage');

$class = $container->getParameter('storage_class'); $sessionStorage = new $class($container->getParameter('session_name')); $user = new User($sessionStorage);

Decoupling

Customization

Objects creation

class Container { protected $parameters = array();

public function __set($key, $value) { $this->parameters[$key] = $value; }

public function __get($key) { return $this->parameters[$key]; } }

Using PHP

magic methods

$container = new Container(); $container->session_name = 'SESSION_ID'; $container->storage_class = 'SessionStorage';

$sessionStorage = new $container->storage_class($container->session_name); $user = new User($sessionStorage);

Interface

is cleaner

DI Container

Managing objects

We need a way to describe how to create objects, without actually instantiating anything!

Anonymous functions to the rescue!

Anonymous Functions / Lambdas

A lambda is a function defined on the fly

with no name

function () { echo 'Hello world!'; };

Anonymous Functions / Lambdas

A lambda can be stored in a variable

$hello = function () { echo 'Hello world!'; };

Anonymous Functions / Lambdas

And then it can be used as any other PHP callable

$hello();

call_user_func($hello);

Anonymous Functions / Lambdas

You can also pass a lambda as an argument to a function or method

function foo(Closure $func) { $func(); }

foo($hello);

Fonctions anonymes $hello = function ($name) { echo 'Hello '.$name; };

$hello('Fabien');

call_user_func($hello, 'Fabien');

function foo(Closure $func, $name) { $func($name); }

foo($hello, 'Fabien');

DI Container

Managing objects

class Container { protected $parameters = array(); protected $objects = array();

public function __set($key, $value) { $this->parameters[$key] = $value; }

public function __get($key) { return $this->parameters[$key]; }

public function setService($key, Closure $service) { $this->objects[$key] = $service; }

public function getService($key) { return $this->objects[$key]($this); } }

Store a lambda

able to create the

object on-demand

Ask the closure to create

the object and pass the

current Container

$container = new Container(); $container->session_name = 'SESSION_ID'; $container->storage_class = 'SessionStorage'; $container->setService('user', function ($c) { return new User($c->getService('storage')); }); $container->setService('storage', function ($c) { return new $c->storage_class($c->session_name); });

$user = $container->getService('user');

Creating the User

is now as easy as before

Description

class Container { protected $values = array();

function __set($id, $value) { $this->values[$id] = $value; }

function __get($id) { if (is_callable($this->values[$id])) { return $this->values[$id]($this); } else { return $this->values[$id]; } } }

Simplify the code

$container = new Container(); $container->session_name = 'SESSION_ID'; $container->storage_class = 'SessionStorage'; $container->user = function ($c) { return new User($c->storage); }; $container->storage = function ($c) { return new $c->storage_class($c->session_name); };

$user = $container->user;

Unified interface

DI Container

Scope

For some objects, like the user, the container must always return the same instance

spl_object_hash($container->user)

!== spl_object_hash($container->user)

$container->user = function ($c) { static $user;

if (is_null($user)) { $user = new User($c->storage); }

return $user; };

spl_object_hash($container->user)

=== spl_object_hash($container->user)

$container->user = $container->asShared(function ($c) { return new User($c->storage); });

A closure is a lambda that remembers the context

of its creation…

class Article { public function __construct($title) { $this->title = $title; }

public function getTitle() { return $this->title; } }

$articles = array( new Article('Title 1'), new Article('Title 2'), );

$mapper = function ($article) { return $article->getTitle(); };

$titles = array_map($mapper, $articles);

$method = 'getTitle';

$mapper = function ($article) use($method) { return $article->$method(); };

$method = 'getAuthor';

$titles = array_map($mapper, $articles);

$mapper = function ($method) { return function ($article) use($method) { return $article->$method(); }; };

$titles = array_map($mapper('getTitle'), $articles);

$authors = array_map($mapper('getAuthor'), $articles);

$container->user = $container->asShared(function ($c) { return new User($c->storage); });

function asShared(Closure $lambda) { return function ($container) use ($lambda) { static $object;

if (is_null($object)) { $object = $lambda($container); } return $object; }; }

class Container { protected $values = array();

function __set($id, $value) { $this->values[$id] = $value; }

function __get($id) { if (!isset($this->values[$id])) { throw new InvalidArgumentException(sprintf('Value "%s" is not defined.', $id)); }

if (is_callable($this->values[$id])) { return $this->values[$id]($this); } else { return $this->values[$id]; } } }

Error management

class Container { protected $values = array();

function __set($id, $value) { $this->values[$id] = $value; }

function __get($id) { if (!isset($this->values[$id])) { throw new InvalidArgumentException(sprintf('Value "%s" is not defined.', $id)); }

if (is_callable($this->values[$id])) { return $this->values[$id]($this); } else { return $this->values[$id]; } }

function asShared($callable) { return function ($c) use ($callable) { static $object;

if (is_null($object)) { $object = $callable($c); } return $object; }; } }

40 LOC for a fully-

featured container

More about Dependency Injection

http://fabien.potencier.org/article/17/on-php-5-3-lambda-functions-and-closures

http://components.symfony-project.org/dependency-injection/

http://github.com/fabpot/pimple

http://twittee.org/

Twittee: A Container in a tweet

•  Implementation does not use PHP 5.3 •  Its usage needs PHP 5.3

class Container { protected $s=array(); function __set($k, $c) { $this->s[$k]=$c; } function __get($k) { return $this->s[$k]($this); } }

twittee.org

Remember, most of the time, you don’t need a Container

to use Dependency Injection

You can start to use and benefit from Dependency Injection today

by implementing it in your projects

by using externals libraries that already use DI

without the need of a container

Symfony Zend Framework ezComponents

Doctrine Swift Mailer

…

Questions?

My slides will be available on slideshare.com/fabpot

with Matthew Weier O’Pheinney

I will reveal the first alpha release of Symfony 2.0!

symfony-live.com

with Matthew Weier O’Pheinney

… with Matthew Weier O'Phinney as a special guest

symfony-live.com

Sensio S.A. 92-98, boulevard Victor Hugo

92 115 Clichy Cedex FRANCE

Tél. : +33 1 40 99 80 80

Contact Fabien Potencier

fabien.potencier at sensio.com

http://www.sensiolabs.com/

http://www.symfony-project.org/

http://fabien.potencier.org/

Symfony Components Dependency Injection

BONUS

Symfony\Components\DependencyInjection

use Symfony\Components\DependencyInjection\Builder; use Symfony\Components\DependencyInjection\Reference;

$container = new Builder();

$container->register('output', 'FancyOutput');

$container-> register('message', 'Message')-> setArguments(array(new Reference('output'), array('with_newline' => true))) ;

$container->message->say('Hello World!');

DI Container Hello World example

Get the configuration for the message service

The Message constructor must be given an output service

Get the output object from the container

Create a Message object by passing the constructor arguments

$message = $container->message;

$message = $container->message;

is roughly equivalent to

$output = new FancyOutput(); $message = new Message($output, array('with_newline' => true));!

$container = new Builder();

$container->register('output', 'FancyOutput'); $container-> register('message', 'Message')-> setArguments(array(new Reference('output'), array('with_newline' => true))) ;

$container->message->say('Hello World!');

<container xmlns="http://symfony-project.org/2.0/container"> <services> <service id="output" class="FancyOutput" />

<service id="message" class="Message"> <argument type="service" id="output" /> <argument type="collection"> <argument key="with_newline">true</argument> </argument> </service> </services> </container>

$container = new Builder(); $loader = new XmlFileLoader($container); $loader->load('services.xml');

PHP

XML XML is validated against an XSD

$container = new Builder();

$container->register('output', 'FancyOutput'); $container-> register('message', 'Message')-> setArguments(array(new sfServiceReference('output'), array('with_newline' => true))) ;

$container->message->say('Hello World!');

services: output: { class: FancyOutput } message: class: Message arguments: - @output - { with_newline: true }

$container = new Builder(); $loader = new YamlFileLoader($container); $loader->load('services.yml');

PHP

YAML

<container xmlns="http://symfony-project.org/2.0/container"> <parameters> <parameter key="output.class">FancyOutput</parameter> <parameter key="message.options" type="collection"> <parameter key="with_newline">true</parameter> </parameter> </parameters>

<services> <service id="output" class="%output.class%" />

<service id="message" class="Message"> <argument type="service" id="output" /> <argument>%message.options%</argument> </service> </services> </container>

$container = new Builder(); $loader = new XmlFileLoader($container); $loader->load('services.xml');

<container xmlns="http://symfony-project.org/2.0/container"> <imports> <import resource="config.xml" /> </imports>

<services> <service id="output" class="%output.class%" /> <service id="message" class="Message"> <argument type="service" id="output" /> <argument>%message.options%</argument> </service> </services> </container>

<container xmlns="http://symfony-project.org/2.0/container"> <parameters> <parameter key="output.class">FancyOutput</parameter> <parameter key="message.options" type="collection"> <parameter key="with_newline">true</parameter> </parameter> </parameters> </container>

$container = new Builder(); $loader = new FileXmlFileLoader($container); $loader->load('services.xml');

<services> <import resource="config.yml" class="Symfony\Components\DependencyInjection\Loader\YamlFileLoader" />

<service id="output" class="%output.class%" /> <service id="message" class="Message"> <argument type="service" id="output" /> <argument>%message.options%</argument> </service> </services>

parameters: output.class: FancyOutput

message.options: { with_newline: true }

$container = new Builder(); $loader = new XmlFileLoader($container); $loader->load('services.xml');

Loaders & Dumpers

•  IniFileLoader •  XmlFileLoader •  YamlFileLoader

•  XmlDumper •  YamlDumper •  PhpDumper •  GraphvizDumper

Make your container VERY fast

use Symfony\Components\DependencyInjection\Builder; use Symfony\Components\DependencyInjection\Reference; use Symfony\Components\DependencyInjection\Dumper\XmlDumper; use Symfony\Components\DependencyInjection\Dumper\YamlDumper; use Symfony\Components\DependencyInjection\Dumper\PhpDumper; use Symfony\Components\DependencyInjection\Loader\XmlFileLoader; use Symfony\Components\DependencyInjection\Loader\YamlFileLoader;

$container = new Builder();

$container->register('output', 'FancyOutput');

$container-> register('message', 'Message')-> setArguments(array(new Reference('output'), array('with_newline' => true))) ;

$dumper = new XmlDumper($container); file_put_contents(__DIR__.'/container.xml', $dumper->dump());

$loader = new XmlFileLoader($container); $loader->load(__DIR__.'/container.xml');

$dumper = new YamlDumper($container); file_put_contents(__DIR__.'/container.yml', $dumper->dump());

$loader = new YamlFileLoader($container); $loader->load(__DIR__.'/container.yml');

$dumper = new PhpDumper($container); echo $dumper->dump();

use Symfony\Components\DependencyInjection\Container; use Symfony\Components\DependencyInjection\Reference; use Symfony\Components\DependencyInjection\Parameter;

class ProjectServiceContainer extends Container { protected $shared = array();

protected function getOutputService() { if (isset($this->shared['output'])) return $this->shared['output'];

$instance = new FancyOutput();

return $this->shared['output'] = $instance; }

protected function getMessageService() { if (isset($this->shared['message'])) return $this->shared['message'];

$instance = new Message($this->getService('output'), array('with_newline' => true));

return $this->shared['message'] = $instance; } }

use Symfony\Components\DependencyInjection\Dumper\GraphvizDumper;

$dumper = new GraphvizDumper($container); echo $dumper->dump();

digraph sc { ratio="compress" node [fontsize="11" fontname="Arial" shape="record"]; edge [fontsize="9" fontname="Arial" color="grey" arrowhead="open" arrowsize="0.5"];

node_output [label="output\nFancyOutput\n", shape=record, fillcolor="#eeeeee", style="filled"]; node_message [label="message\nMessage\n", shape=record, fillcolor="#eeeeee", style="filled"]; node_service_container [label="service_container\nSymfony\\Components\\DependencyInjection\\Builder\n", shape=record, fillcolor="#9999ff", style="filled"]; node_message -> node_output [label="" style="filled"]; }