OOP for Drupal Developers

Introduction to Object-Oriented PHP for DrupalCon Amsterdam

Transcript

2. What?
3. What is OOP? Object orientation is the computer science of long words lornajane
4. OOP Glossary • methods these are functions. Seriously • properties these are variables • class recipe for making an object • object cool thing with its own properties and methods
5. Why?
6. Encapsulation In OOP: • array indexes become “properties” • functions lose their prefix and become “methods” An object contains both data and functionality
7. Encapsulation Imagine an array of data $date = array("hours" => "14", "minutes" => "36", "timezone" => "Europe/Amsterdam"); And some functions date_get_timestamp($date); date_get_time($date); date_get_datetime_in_timezone($date, $tz);
8. Autoloading Code in classes can be autoloaded. This means: • you will never write another require() statement • only the code actually needed will ever be parsed
9. How Autoloading Works
10. Prerequisites for Autoloading • one class per file • very predictable mapping from namespaced classname to file location • e.g. \MyLib\User lives in lib/MyLib/User.php For more details, see PSR4: http://www.php-fig.org/psr/psr-4/
11. Write an Autoloader Write a function which accepts the classname and includes the relevant file. To tell PHP about your autoloader: spl_autoload_register("my_autoload_func");
12. Extendable We can take an object, and just change one bit or add something, without copy pasting. The keyword is “inheritance”
13. Inheritance Take this ClickableButton class and make it go ping when clicked. class PingingButton extends ClickableButton Our new class gets everything that was in ClickableButton and we can add/override as we wish
14. Pluggable Code expecting one type of object can easily accept a similar one. We can extend or replace objects without changing the code that handles it.
15. How?
16. Start With a Class We’ll create a class with properties and methods.
17. PHP User Class Start by declaring the class and its properties … 1 class User { 2 protected $username; 3 protected $email;
18. PHP User Class … next the constructor … 1 public function __construct($username) { 2 // lookup table for people's details 3 $people = [ 4 "lornajane" => "lorna@lornajane.net", 5 "crell" => "larry@...", 6 "emmajanehw" => "emma@..." 7 ]; 8 9 $this->username = $username; 10 $this->email = $people[$username]; 11 12 }
19. PHP User Class … and a couple of other methods 1 public function getUsername() { 2 return $this->username; 3 } 4 5 public function getGravatar() { 6 $url = "http://www.gravatar.com/avatar/" 7 . md5($this->email); 8 return "<img src=\"$url\">"; 9 } 10 }
20. How to Use a Class First we need to require or autoload the code. Then we instantiate the object.
21. Autoloader spl_autoload_register(function ($classname) { require __DIR__ . '/../inc/' . $classname . '.php'; });
22. Instantiate a User Object Create an object by using the new keyword $user = new User("lornajane");
23. User Object in a Template This is what I have in my template file <?=$user->getGravatar()?> Hi, <?=$user->getUsername()?>
24. Project Overview . ├── inc │ └── User.php ├── public │ └── index.php ├── README.md └── templates ├── footer.php ├── greet.php ├── header.php └── login.php
25. Look What We Made
26. Look What We Made
27. And Breathe
28. Other Cool OOP Things • inheritance • namespaces • interfaces • exceptions
29. Inheritance We have a User class. How about something a little more specific? 1 class AdminUser extends User { 2 public function getUsername() { 3 $name = parent::getUsername(); 4 return $name . " (admin)"; 5 } 6 }
30. Use the Admin Class If the user ticked the box, we stored that too 1 if($_SESSION['admin']) { 2 $user = new AdminUser($_SESSION['username']); 3 } else { 4 $user = new User($_SESSION['username']); 5 }
31. Now Look
32. Now Look
33. What About StdClass? The StdClass class is just the parent of all other objects in PHP It’s better to declare a class for a specific use
34. Namespaces Namespaces allow us to separate our code, and use multiple libraries
35. Namespaces We change class declarations and rename files to match inc/User.php becomes inc/User/User.php namespace User; class User { inc/AdminUser.php becomes inc/User/Admin.php namespace User; class Admin extends User {
36. Project Overview . ├── inc │ ├── Animal │ │ └── Cat.php │ └── User │ ├── Admin.php │ └── User.php ├── public │ └── index.php ├── README.md └── templates └── ...
37. Namespaces The autoloader needs to change as well 1 spl_autoload_register(function ($classname) { 2 require __DIR__ . '/../inc/' 3 . str_replace('\\', DIRECTORY_SEPARATOR, $classname) 4 . '.php'; 5 });
38. Namespaces We also need to give the qualified name of the object when instantiating it: $user = new \User\User("lornajane");
39. Namespaces New classes can go into new namespaces 1 namespace Animal; 2 3 class Cat { 4 protected $username; 5 protected $email; 6 7 public function __construct() { 8 // I only know one cat 9 $this->username = "orbit"; 10 $this->email = "orbit@lornajane.net"; 11 }
40. Using Another Object Let’s instantiate and use some objects // featured users $featured = array( new \User\User("emmajanehw"), new \Animal\Cat()); <h2>Other Excellent Users Of This Site:</h2> <?php foreach($featured as $user): ?> <?=$user->getGravatar()?>&nbsp; <?php endforeach; ?>
41. Showing Off Featured Users
42. Object Identity How can we check if an object has a getGravatar() method?
43. Object Identity How can we check if an object has a getGravatar() method? Check the object type with instanceof • but one is a Cat and one is a User, and what if we add more types?
44. Interfaces An interface is a contract. It defines what an object can do. We could make a Picturesque interface interface Picturesque { public function getGravatar(); } Good news: autoloading works for interfaces!
45. Interfaces A Class an implement an interface. Class Cat implements Picturesque If it does, it MUST have all the methods defined exactly as in the interface. (ours already do)
46. Object Identity How can we check if an object has a getGravatar() method? Check the object type with instanceof • but one is a Cat and one is a User, and what if we add more types?
47. Object Identity How can we check if an object has a getGravatar() method? Check the object type with instanceof • but one is a Cat and one is a User, and what if we add more types? Only accept objects which implement the Picturesque interface
48. TypeHinting How to require that a particular interface is used function addFeaturedUser(Picturesque $user) { return $user; } Adapt our code to use this function // featured users $featured[] = addFeaturedUser(new \User\User("emmajanehw")); $featured[] = addFeaturedUser(new \Animal\Cat());
49. Exceptions Exceptions are: • beautiful errors • objects • opportunities
50. Exceptions in PHP Exceptions are Objects; they can be extended PHP itself throws exceptions: $db = new PDO("foo", "bar"); PHP Fatal error: Uncaught exception ‘PDOExceptio with message ‘invalid data source name’
51. Exceptions in PHP We should catch exceptions: 1 try { 2 // success case code goes here 3 $db = new PDO("foo", "bar"); 4 } catch(PDOException $e) { 5 echo "some DB fail occurred"; 6 }
52. Throwing Exceptions function addTwoNumbers($a, $b) { if(($a == 0) || ($b == 0)) { throw new Exception("Zero is Boring!"); } return $a + $b; } echo addTwoNumbers(3,2); // 5 echo addTwoNumbers(5,0); // error!! Fatal error: Uncaught exception 'Exception' with message 'Zero is Boring!'
53. Extending Exceptions We can extend the Exception class for our own use 1 class DontBeDaftException extends Exception { 2 } 3 4 function inspectCurtains($colour) { 5 if($colour == "orange" || $colour == "spotty") { 6 throw new DontBeDaftException($colour . 'is daft'); 7 } 8 echo "The curtains are $colour\n"; 9 }
54. And Breathe
55. And Breathe (just one more thing)
56. Duplicate Functionality Did you notice that the getGravatar() method is identical in those unrelated classes?
57. Traits Traits are simply compiler-assisted copy/paste. Rasmus Lerdorf
58. Traits A trait looks a lot like a class, or a bit of one 1 trait Gravatar { 2 public function getGravatar() { 3 $url = "http://www.gravatar.com/avatar/" 4 . md5($this->email); 5 return "<img src=\"$url\">"; 6 } 7 } Good news: autoloading works for traits!
59. Traits Put a trait into your class with the use keyword: 1 namespace User; 2 3 class User implements \Picturesque { 4 protected $username; 5 protected $email; 6 7 use \Gravatar; 8 9 public function __construct($username) { 10 ....
60. Project Overview . ├── inc │ ├── Animal │ │ └── Cat.php │ ├── Gravatar.php │ ├── Picturesque.php │ └── User │ ├── Admin.php │ └── User.php ├── public │ └── index.php ├── README.md └── templates └── ...
61. That’s all, folks
62. TL;DR • class recipe for making an object • object an item with properties and methods • inheritance use one class as basis for another • interface contract agreeement for classes • typehinting how to identify a class • trait how to use the same functionality in two unrelated classes
63. Questions? (and resources) Intermediate PHP http://lrnja.net/php-video Contact me: @lornajane or http://lornajane.net