Dependency Injection and Dependency Inversion in PHP

Dependency Injection and Dependency Inversion are important tools for writing testable and reusable code. They are available in any object oriented language and PHP is no exception. In this talk we will look at both Dependency Injection and the Dependency Inversion Principle, how they fit in with SOLID, and why they should be used when writing object oriented code. How are objects wired together? What is an object graph? Is a Dependency Injection Container the right way forward? Can we do this automatically, and are there any patterns or reusable components available to help us achieve reusable and decoupled code? These are some of the topics covered in this talk from both a theoretical and a practical standpoint. Walking out of the room you should understand why dependency injection is so heavily advocated in programming and how you can use it to write awesome, decoupled code in PHP.

Transcript

1. Dependency Injection and Dependency Inversion in PHP @J7mbo
2. Your goal on a project?
3. Professional Integrity
4. “I want a plumber who takes a pride in his work, who bothers to learn and gain experience, who takes what he does seriously” “I expect to pay extra for expertise, but it's a wise investment compared to hiring a cowboy plumber and having to pay later to fix up the botch job he left me with”
5. “Integrity is "doing the right thing even when no one is looking", and I see Software Craftsmanship as striving for integrity in the systems we create.” David Starr (elegantcode.com)
7. A little bit about me…
8. OOP, DI, DiP, IoC, DIC, SOLID, WTF
17. Object Instantiation
18. Object Instantiation Http Request
19. Object Instantiation Http Request Disgusting DOM Searching
20. Object Instantiation Http Request Disgusting DOM Searching Sorting Algorithm
22. Please be True…
25. Asking for objects to be passed in is Dependency Injection Calling Code
26. Inversion of Control
27. I have to mock this… And this… This too.. srsly
28. Calling getContents() will now return this HTML Passing in my $fakeClient
29. Dependency Injection provides Control
30. 1 year later…
31. “High-level modules should not depend on low-level modules. Both should depend on abstractions”
34. “Polymorphism is the provision of a single interface to entities of different types”
35. Recap • Dependency Injection is simply passing in object dependencies as parameters instead of instantiating them in the object using them
36. Recap • Dependency Injection is simply passing in object dependencies as parameters instead of instantiating them in the object using them • Doing this gives you Inversion of Control, as the control over object creation is no longer delegated to the object using them
37. Recap • Dependency Injection is simply passing in object dependencies as parameters instead of instantiating them in the object using them • Doing this gives you Inversion of Control, as the control over object creation is no longer delegated to the object using them • If you use don’t do this, other people will hate you because they can’t mock your objects easily in their tests (so your code is not testable)
38. Recap • Dependency Injection is simply passing in object dependencies as parameters instead of instantiating them in the object using them • Doing this gives you Inversion of Control, as the control over object creation is no longer delegated to the object using them • Using interfaces, we can adhere to the Dependency Inversion Principle and depend on abstractions • If you use don’t do this, other people will hate you because they can’t mock your objects easily in their tests (so your code is not testable)
39. Recap • Dependency Injection is simply passing in object dependencies as parameters instead of instantiating them in the object using them • Doing this gives you Inversion of Control, as the control over object creation is no longer delegated to the object using them • Using interfaces, we can adhere to the Dependency Inversion Principle and depend on abstractions • Code always starts off procedural, and builds objects up before executing them in an object oriented manner • If you use don’t do this, other people will hate you because they can’t mock your objects easily in their tests (so your code is not testable)
41. Bootstrap (Procedural) Framework (Object Oriented) (hopefully) Dev Code (Object Oriented) (hopefully) Composition Root Objects built
42. Bootstrap (Procedural) Framework (Object Oriented) (hopefully) Dev Code (Object Oriented) (hopefully) Composition Root Objects built Match route to controller + action Create controller Run action with any request parameters
43. Bootstrap (Procedural) Framework (Object Oriented) (hopefully) Dev Code (Object Oriented) (hopefully) Composition Root Objects built Match route to controller + action Create controller Run action with any request parameters Developer creates a controller Does whatever they want
44. Framework (Object Oriented) (hopefully)
45. Framework (Object Oriented) (hopefully)
46. Dependency Injection Container (DiC)
47. Get the Conference object here
48. External requirements should be visible from an object’s constructor and method signatures
49. Bootstrap (Procedural) Framework (Object Oriented) (hopefully) Dev Code (Object Oriented) (hopefully) Composition Root Objects defined and registed in container ‘Object Graph’
50. Bootstrap (Procedural) Framework (Object Oriented) (hopefully) Dev Code (Object Oriented) (hopefully) Composition Root Objects defined and registed in container Match route to controller + action Container Creates controller (with dependencies) Container runs action with any request parameters ‘Object Graph’
51. Bootstrap (Procedural) Framework (Object Oriented) (hopefully) Dev Code (Object Oriented) (hopefully) Composition Root Objects defined and registed in container Match route to controller + action Container Creates controller (with dependencies) Container runs action with any request parameters Developer creates a controller DI’s registered dependencies Does whatever they want ‘Object Graph’
55. Create the PhpNw15Conference object
60. Automatic Injection for concrete classes
63. See ‘Conference’ Create ‘PhpNw15Conference’
66. Bootstrap (Procedural) Framework (Object Oriented) (hopefully) Dev Code (Object Oriented) (hopefully) Composition Root Relationships (object graph) defined in configuration file Match route to controller + action Injector Creates controller (with dependencies) Developer creates a controller DI’s registered dependencies Does whatever they want
67. Dev Code (Object Oriented) (hopefully) Developer creates a controller DI’s registered dependencies Does whatever they want
68. Dev Code (Object Oriented) (hopefully) Developer creates a controller DI’s registered dependencies Does whatever they want
69. Dev Code (Object Oriented) (hopefully) Developer creates a controller DI’s registered dependencies Does whatever they want • Not coupled to container • Remove code / move code about at any time • Concentrate on writing SOLID code
72. • Your objects should specify external requirements needed in their constructor and method signatures
73. • Your objects should specify external requirements needed in their constructor and method signatures • Dependency Injection is simply passing in external requirements as parameters
74. • Your objects should specify external requirements needed in their constructor and method signatures • Dependency Injection is simply passing in external requirements as parameters • Using interfaces for functionality that might change provides polymorphism (switch out concrete implementation any time)
75. • Your objects should specify external requirements needed in their constructor and method signatures • Dependency Injection is simply passing in external requirements as parameters • Using interfaces for functionality that might change provides polymorphism (switch out concrete implementation any time) • Depending on abstractions rather than concretes (interfaces), and having your object graph composed ‘higher’ in the codebase (composition root), provides Inversion of Control and helps you adhere to the Dependency Inversion Principle
76. What next? AOP and PHP7’s Anonymous Classes
77. ‘Decorate’ existing Controller Delegate controller method call,
 but add additional functionality (logging)
81. Anonymous Class Automatic
 Decoration
82. How can I apply this? • Choose a framework that supports automatic recursive DI • Choose a micro-framework or components that allow you to substitute the ‘controller resolver’ to provide this • Legacy codebase? Don’t have to use an auto-injector, just design your interfaces well adhere to DIP when you can • In your next project, make this a primary consideration of your software architecture
83. Why bother?
84. • The ‘gang of four book’ (GoF) • The Clean Coder (Robert C. Martin) • Post your code on CodeReview (and survive)
85. @J7mbo https://joind.in/talk/view/15431