dependency injection in php
DESCRIPTION
Slides from my talk during PHPCon Poland. Szczyrk 25/10/2013TRANSCRIPT
Dependency Injection in PHP
PHPCon Poland Szczyrk 25/10/13
!by @cakper
flickr.com/limowreck666/223731385/
Kacper Gunia // @cakper
Software Engineer @SensioLabsUK
Symfony Certified Developer
#Symfony-PL // SymfonyLab.pl
Silesian PHP User Group // SPUG.pl
Inversion of Control
Dependency Injection
Events
Aspect Oriented Programming
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Diving into Dependency Injection
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Dependency Injection!!class DvdPlayer { public function playDisc(Disc $disc) { echo 'Now playing: '.$disc-‐>getMovieTitle(); ! $tv = new Tv('Samsung 40"'); $tv-‐>sendToOutput($disc-‐>getResource()); } }
Dependency Injectionclass DvdPlayer { private $tv; ! public function __construct() { $this-‐>tv = new Tv('Samsung 40"');; } ! public function playDisc(Disc $disc) { echo 'Now playing: ' . $disc-‐>getMovieTitle(); $this-‐>tv-‐>sendToOutput($disc-‐>getResource()); } }
Dependency Injectionclass DvdPlayer { private $tv; ! public function __construct(Tv $tv) { $this-‐>tv = $tv; } // (...) } !$tv = new Tv('Samsung 40"'); $dvdPlayer = new DvdPlayer($tv);
Dependency Injectionclass DvdPlayer { private $device; ! public function __construct(HdmiDevice $device) { $this-‐>device = $device; } // (...) } !$projector = new Projector('Epson EB'); $dvdPlayer = new DvdPlayer($tv);
Nailed it!
“Dependency Injection is where components are given
their dependencies through their constructors, methods, or
directly into fields.”
!
“(...) it is a 25-dollar term for a 5-cent concept”
source: picocontainer.codehaus.org jamesshore.com
Types of Injection
Constructor
Setter
Property
Reflection
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Constructor Injection
class Tv implements HdmiDevice{} class DvdPlayer { private $device; ! public function __construct(HdmiDevice $device) { $this-‐>device = $device; } } !$tv = new Tv('Samsung 40"'); $dvdPlayer = new DvdPlayer($tv);
Setter Injection
class BlurayDisc implements Disc{} class DvdPlayer { private $disc; ! public function setDisc(Disc $disc) { $this-‐>disc = $disc; } } !$disc = new BlurayDisc('Pulp Fiction'); $dvdPlayer = new DvdPlayer(); $dvdPlayer-‐>setDisc($disc);
Property Injection
class DvdPlayer { public $remote; } !$dvdPlayer = new DvdPlayer(); $dvdPlayer-‐>remote = new Remote();
Reflection Injection
class DvdPlayer { private $powerSupply; } !$dvdPlayer = new DvdPlayer(); $reflector = new ReflectionClass($dvdPlayer); $powerSupply = $reflector-‐>getProperty('powerSupply'); $powerSupply-‐>setAccessible(true); !$powerSupply-‐>setValue($dvdPlayer, new PowerSupply());
Pros & Cons
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Decoupling
Advantage #1
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Dependency Inversion Principle
Advantage #2
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Reusability
Advantage #3
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Clean code
Advantage #4
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Easier testing
Advantage #5
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Instance management
Advantage #6
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IDE support
Advantage #7
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Complex initialisation
Disadvantage
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Factory
Simple Solution
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Dependency Injection Container
Proper Solution
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“Dependency Injection Container is simply a PHP
object that manages the instantiation of other objects”
!
We call them “Services”
source: symfony.com
Our DvdPlayer
!!$tv = new Tv('Samsung 40"'); $dvdPlayer = new DvdPlayer($tv); !$disc = new Disc('Pulp Fiction'); $dvdPlayer-‐>playDisc($disc);
Simple Container class
class Container { public function getTv() { return new Tv('Samsung 40"'); } ! public function getDvdPlayer() { return new DvdPlayer($this-‐>getTv()); } }
Container use
!!$container = new Container(); !$dvdPlayer = $container-‐>getDvdPlayer(); !$disc = new Disc('Pulp Fiction'); $dvdPlayer-‐>playDisc($disc);
DIC ImplementationsTwitteePimplePHP-DI Zend\DiIlluminate\ContainerOrno\DiLeague\DiSymfony\DependencyInjection
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DI & DIC Patterns
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Expect Interfaces, not Implementations
Pattern #1
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Don’t check null values
Pattern #2
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class DvdPlayer { public $disc; ! public function play() { if (!is_null($this-‐>disc)) { $this-‐>sendToOutput($this-‐>disc-‐>getResource()); } } ! public function play() { if ($this-‐>disc instanceof Disc) { $this-‐>sendToOutput($this-‐>disc-‐>getResource()); } } }
Avoid ‘Service Locator’
Pattern #3
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class DvdPlayer { private $locator; ! public function __construct() { $this-‐>locator = ServiceLocator::getInstance(); } !! public function playDisc(Disc $disc) { $this-‐>locator -‐>getTv() -‐>sendToOutput($disc-‐>getResource()); } }
Don’t inject whole container
Pattern #4
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In DIC store Services and Properties,
but not Entities
Pattern #5
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Don’t be afraid to create plenty of small Classes
Pattern #6
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Symfony DIC in action
Services
new Tv('Samsung 40”’) !services: tv: class: Tv arguments: [“Samsung 40"”]
Parameters
new Tv('Samsung 40”’) !parameters: tv_name: Samsung 40"
Parameters & Services
new Tv('Samsung 40”’) !parameters: tv_name: Samsung 40" !services: tv: class: Tv arguments: [“%tv_name%”] !$container-‐>get('tv');
Compiled Container
!!!!protected function getTvService() { return $this-‐>services['tv'] = new \Tv('Samsung'); }
Static Factory
services: tv class: Tv factory_class: TvFactory factory_method: get
Factory
services: tv_factory: class: TvFactory tv class: Tv factory_service: tv_factory factory_method: get
Optional Dependencies
class DvdPlayer { function __construct(HdmiDevice $device = null){} } !services: tv: class: Tv arguments: [%tv_name%] dvd_player: class: DvdPlayer arguments ["@?tv"]
Lazy-loaded Services
services: tv: class: Tv arguments: [“%tv_name%”] lazy: true
Private Services
services: drm_decryptor: class: DrmDecryptor public: false dvd_player: class: DvdPlayer arguments [“@drm_decryptor”]
Scopes
services: tv: class: Tv arguments: [“%tv_name%”] scope: prototype
PHPStorm support
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Adrien Brault
