This document provides an introduction to dependency injection containers (DIC). It begins by explaining dependency injection and its benefits over direct instantiation, such as easier testing and replacing dependencies. It then introduces the concept of a dependency injection container, which manages object instantiation and wiring of dependencies. Using a container allows configuring services differently for production versus development and avoids deeply nested instantiation code. The document demonstrates implementing a simple DI container and using it to resolve object graphs in place of direct construction.

1. Introduction to DI(C)
meet.php #5 http://meetphp.pl/ 19.05.2012

2. About me
$speaker = new Speaker;
$speaker->name = "Radosław Benkel";
$speaker->twitter = "@singlespl";
$speaker->blog = "http://blog.rbenkel.me";
$speaker->givePresentation();

3. What?

4. What?
Dependency
Injection
Container

5. What?
Dependency

6. Dependency
class TwitterAPIClient
{
protected $httpClient;
public function __construct()
{
$this->httpClient = new SomeCurlWrapper();
}
/* ... */
}
$client = new TwitterApiClient;

7. Dependency
This

8. is

9. your

10. dependency.
class TwitterAPIClient
{
protected $httpClient;
public function __construct()
{
$this-httpClient = new SomeCurlWrapper();
}
/* ... */
}
$client = new TwitterApiClient;

11. Dependency
“What’s

12. wrong

13. with

14.
that”?

15. Dependency
Try testing it...

16. Dependency
...or change client
implementation

17. Dependency

18. Dependency
So let’s use Injection

19. What?
Injection

20. Injection
class TwitterAPIClient
{
protected $httpClient;
public function __construct($httpClient)
{
$this-httpClient = $httpClient;
}
/* ... */
} And

21. here

22. you

23. inject

24. dependency
$client = new TwitterApiClient(new SomeCurlWrapper);

25. Injection
So...

26. Injection
public function __construct()
{
$this-httpClient = new SomeCurlWrapper();
}
VS
public function __construct($httpClient)
{
$this-httpClient = $httpClient;
}

27. Injection
it’s just like...

28. Injection
VS

29. Injection
VS
Try

30. replacing

31. battery,

32. and

33. you

34. will

35. now

36. what

37. I’m

38. talking

39.
about.

41. Injection
Injection types:

42. Injection
Injection types:
• constructor injection

43. Injection
Injection types:
• constructor injection
• setter injection

44. Injection
Injection types:
• constructor injection
• setter injection
• interface injection

45. Injection
Constructor injection
class TwitterAPIClient
{
protected $httpClient;
public function __construct($httpClient)
{
$this-httpClient = $httpClient;
}
/* ... */
}
$client = new TwitterApiClient(new SomeCurlWrapper);

46. Injection
Setter injection
class TwitterAPIClient
{
protected $httpClient;
public function __construct() {}
public function setHttpClient($httpClient) {
$this-httpClient = $httpClient;
}
/* ... */
}
$client = new TwitterApiClient;
$client-setHttpClient(new SomeCurlWrapper);

47. Injection
Interface injection
interface HttpClientInterface {
public function setHttpClient($httpClient);
}
class TwitterAPIClient implements HttpClientInterface {
protected $httpClient;
public function __construct() {}
public function setHttpClient($httpClient) {
$this-httpClient = $httpClient;
}
/* ... */
}
$client = new TwitterApiClient;
$client-setHttpClient(new SomeCurlWrapper);

48. Injection
So far so good...

49. Injection
...until you don’t have
to do something like
that:

50. Injection
$mapper = new UserMapperEncrypted(
new UserMapperCached(
new UserMapperDB(
new PDO(
'mysql:host=127.0.0.1',
'user',
'password'
)
),
new RedisCacheAdapter(
'127.0.0.1:6379'
)
),
'YourSuperSecretPass'
);
$mapper-save(new User('John', 'Doe'));

51. Injection

52. Injection
“How

53. to

54. solve

55. that”?

56. Injection
Just use...

57. What?
Container

58. Container
require_once container_prod.php;
$mapper = $container-get('mapper.user');
/* mapper is UserMapperEncrypted, which uses UserMapperCached,
which uses UserMapperDB, which uses PDO. */
$mapper-save(new User('John', 'Doe'));

59. Container
require_once container_dev.php;
$mapper = $container-get('mapper.user');
/* mapper is UserMapperDB, with different PDO configuration.
*/
$mapper-save(new User('John', 'Doe'));

60. Container
require_once container_prod.php;
$mapper = $container-get('mapper.user');
$mapper-save(new User('John', 'Doe'));
Find

61. the

62. difference
require_once container_dev.php;
$mapper = $container-get('mapper.user');
$mapper-save(new User('John', 'Doe'));

63. Container
require_once container_prod.php;
$mapper = $container-get('mapper.user');
$mapper-save(new User('John', 'Doe'));
require_once container_dev.php;
$mapper = $container-get('mapper.user');
$mapper-save(new User('John', 'Doe'));

64. Container
require_once container_prod.php;
$mapper = $container-get('mapper.user');
$mapper-save(new User('John', 'Doe'));
Find

65. the

66. difference
Configures

67. services

68. in

69. different

70. way,

71. but

72.
for

73. you,

74. API

75. for

76. mapper

77. is

78. the

79. same.
require_once container_dev.php;
$mapper = $container-get('mapper.user');
$mapper-save(new User('John', 'Doe'));

80. Container
require_once container_prod.php;
$mapper = $container-get('mapper.user');
$mapper-save(new User('John', 'Doe'));
*

81. Assuming,

82. tthe

83. difference the

84.
Find

85. hat

86. all

87. mappers

88. share

89.
same

90. interface,

91. which

92. they

93. rather

94. should.
require_once container_dev.php;
$mapper = $container-get('mapper.user');
$mapper-save(new User('John', 'Doe'));

95. Container
So, DIC it’s something
like:

96. Container

97. Container
What it does:
• injects object dependencies
• creates objects on demand
• objects could be shared
• (and sometimes other stuff, like tagging, XML/
JSON/YAML config etc. )

98. Container
So. Lets write simple
one.

99. Container
class Container
{
protected $items = array();
public function get($key) {
$item = $this-items[$key];
return is_callable($item) ? $item($this) : $item;
}
public function set($key, $value, $shared = false) {
if ($shared === true is_callable($value)) {
$this-items[$key] = function($c) use ($value) {
static $obj;
if (!$obj) {
$obj = $value($c);
}
return $obj;
};
} else {
$this-items[$key] = $value;
}
}
}

100. Container
class Container
{
protected $items = array();
*

101. Inspired

102. by

103. Pimple
public function get($key) {
$item = $this-items[$key];
return is_callable($item) ? $item($this) : $item;
}
public function set($key, $value, $shared = false) {
if ($shared === true is_callable($value)) {
$this-items[$key] = function($c) use ($value) {
static $obj;
if (!$obj) {
$obj = $value($c);
}
return $obj;
};
} else {
$this-items[$key] = $value;
}
}
}

104. Injection
Lets use that.

105. Injection
Replacing this:

106. Injection
$mapper = new UserMapperEncrypted(
new UserMapperCached(
new UserMapperDB(
new PDO(
'mysql:host=127.0.0.1',
'user',
'password'
)
),
new RedisCacheAdapter(
'127.0.0.1:6379'
)
),
'YourSuperSecretPass'
);
$mapper-save(new User('John', 'Doe'));

107. Injection
with this:

108. Injection
require_once container_prod.php;
$mapper = $container-get('mapper.user');
/* mapper is UserMapperEncrypted, which uses UserMapperCached
(using Redis for cache), which uses UserMapperDB, which uses
PDO. */
$mapper-save(new User('John', 'Doe'));

109. Injection
Because everything is
configured in
container...

110. Injection
//container_prod.php
$c = new Container();
$c-set('pdo.dsn', 'mysql:host=127.0.0.1');
$c-set('pdo.user', 'user');
$c-set('pdo.pass', 'password');
$c-set('redis.host', '127.0.0.1:6379');
$c-set('mcrypt.key', 'YourSuperSecretPass');
$c-set('pdo', function(Container $c) {
return new PDO(
$c-get('pdo.dsn'),
$c-get('pdo.user'),
$c-get('pdo.pass'),
);
}, true);
$c-set('cache.adapter', function(Container $c) {
return new RedisCacheAdapter($c-get('redis.host'));
});
$c-set('mapper.user', function(Container $c) {
return new UserMapperEncrypted(
new UserMapperCached(
new UserMapperDB($c-get('pdo')),
$c-get('cache.adapter')
),
$c-get('mcrypt.key')
);
});

111. Injection
...you can change e.g
cache adapter...

112. Injection
//container_prod.php
$c = new Container();
$c-set('pdo.dsn', 'mysql:host=127.0.0.1');
$c-set('pdo.user', 'user');
$c-set('pdo.pass', 'password');
$c-set('mcrypt.key', 'YourSuperSecretPass');
$c-set('pdo', function(Container $c) {
return new PDO(
$c-get('pdo.dsn'),
$c-get('pdo.user'),
$c-get('pdo.pass'),
);
}, true);
$c-set('cache.adapter', function(Container $c) {
return new ApcCacheAdapter();
});
$c-set('mapper.user', function(Container $c) {
return new UserMapperEncrypted(
new UserMapperCached(
new UserMapperDB($c-get('pdo')),
$c-get('cache.adapter')
),
$c-get('mcrypt.key')
);
});

113. Injection
//container_prod.php
$c = new Container();
$c-set('pdo.dsn', 'mysql:host=127.0.0.1');
$c-set('pdo.user', 'user');
$c-set('pdo.pass', 'password');
$c-set('mcrypt.key', 'YourSuperSecretPass');
$c-set('pdo', function(Container $c) {
return new PDO(
$c-get('pdo.dsn'),
$c-get('pdo.user'),
$c-get('pdo.pass'),
);
}, true);
$c-set('cache.adapter', function(Container $c) {
return new ApcCacheAdapter();
});
$c-set('mapper.user', function(Container $c) {
return new UserMapperEncrypted(
new UserMapperCached(
new UserMapperDB($c-get('pdo')),
$c-get('cache.adapter')
),
$c-get('mcrypt.key')
);
});

114. Injection
...and your your code
hasn’t changed at all.

115. Injection
require_once container_prod.php;
$mapper = $container-get('mapper.user');
/* mapper is UserMapperEncrypted, which uses UserMapperCached
(using Apc for cache), which uses UserMapperDB, which uses
PDO. */
$mapper-save(new User('John', 'Doe'));

116. Container
But probably, you
should use another
DIC:

117. Container
• AuraDI
http://auraphp.github.com/Aura.Di/
• Pimple
http://pimple.sensiolabs.org/
• Symfony 2 Dependency Injection Component
http://symfony.com/doc/current/components/dependency_injection/
introduction.html
• ZF2 Dependency Injection
http://framework.zend.com/wiki/display/ZFDEV2/Zend+DI+QuickStart
• Twittee
http://twittee.org/

118. Container
• AuraDI
PHP

119. 5.4

120. only
http://auraphp.github.com/Aura.Di/
• Pimple
http://pimple.sensiolabs.org/
• Symfony 2 Dependency Injection Component
http://symfony.com/doc/current/components/dependency_injection/
introduction.html
• ZF2 Dependency Injection
http://framework.zend.com/wiki/display/ZFDEV2/Zend+DI+QuickStart
• Twittee
http://twittee.org/

121. Container
• AuraDI
http://auraphp.github.com/Aura.Di/
• Pimple
Small,

122. basic
http://pimple.sensiolabs.org/
• Symfony 2 Dependency Injection Component
http://symfony.com/doc/current/components/dependency_injection/
introduction.html
• ZF2 Dependency Injection
http://framework.zend.com/wiki/display/ZFDEV2/Zend+DI+QuickStart
• Twittee
http://twittee.org/

123. Container
• AuraDI
Lot’s

124. of

125. features
http://auraphp.github.com/Aura.Di/
• Pimple
http://pimple.sensiolabs.org/
• Symfony 2 Dependency Injection Component
http://symfony.com/doc/current/components/dependency_injection/
introduction.html
• ZF2 Dependency Injection
http://framework.zend.com/wiki/display/ZFDEV2/Zend+DI+QuickStart
• Twittee
http://twittee.org/

126. Container
• AuraDI
http://auraphp.github.com/Aura.Di/
• Pimple
http://pimple.sensiolabs.org/
• Symfony 2 Dependency Injection Component
http://symfony.com/doc/current/components/dependency_injection/
introduction.html
• ZF2 Dependency Injection
http://framework.zend.com/wiki/display/ZFDEV2/Zend+DI+QuickStart
• Twittee
http://twittee.org/
Fits

127. into

128. tweet!

129. Thank you!