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What?
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What is OOP?
Object orientation is the computer science of long
words
lornajane
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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
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Why?
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Encapsulation
In OOP:
• array indexes become “properties”
• functions lose their prefix and become
“methods”
An object contains both data and functionality
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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);
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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
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How Autoloading Works
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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/
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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");
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Extendable
We can take an object, and just change one bit
or add something, without copy pasting.
The keyword is “inheritance”
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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
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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.
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How?
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Start With a Class
We’ll create a class with properties and
methods.
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PHP User Class
Start by declaring the class and its properties …
1 class User {
2 protected $username;
3 protected $email;
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PHP User Class
… next the constructor …
1 public function __construct($username) {
2 // lookup table for people's details
3 $people = [
4 "lornajane" => "[email protected]",
5 "crell" => "larry@...",
6 "emmajanehw" => "emma@..."
7 ];
8
9 $this->username = $username;
10 $this->email = $people[$username];
11
12 }
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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 "
";
9 }
10 }
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How to Use a Class
First we need to require or autoload the code.
Then we instantiate the object.
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Autoloader
spl_autoload_register(function ($classname) {
require __DIR__ . '/../inc/' . $classname . '.php';
});
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Instantiate a User Object
Create an object by using the new keyword
$user = new User("lornajane");
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User Object in a Template
This is what I have in my template file
getGravatar()?> Hi, getUsername()?>
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Project Overview
.
├── inc
│ └── User.php
├── public
│ └── index.php
├── README.md
└── templates
├── footer.php
├── greet.php
├── header.php
└── login.php
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Look What We Made
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Look What We Made
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And Breathe
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Other Cool OOP Things
• inheritance
• namespaces
• interfaces
• exceptions
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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 $name . " (admin)";
5 }
6 }
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Use the Admin Class
If the user ticked the box, we stored that too
1 if($_SESSION['admin']) {
2 $user = new AdminUser($_SESSION['username']);
3 } else {
4 $user = new User($_SESSION['username']);
5 }
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Now Look
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Now Look
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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
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Namespaces
Namespaces allow us to separate our code, and
use multiple libraries
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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 {
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Project Overview
.
├── inc
│ ├── Animal
│ │ └── Cat.php
│ └── User
│ ├── Admin.php
│ └── User.php
├── public
│ └── index.php
├── README.md
└── templates
└── ...
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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 });
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Namespaces
We also need to give the qualified name of the
object when instantiating it:
$user = new \User\User("lornajane");
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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 = "[email protected]";
11 }
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Using Another Object
Let’s instantiate and use some objects
// featured users
$featured = array(
new \User\User("emmajanehw"),
new \Animal\Cat());
Other Excellent Users Of This Site:
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Showing Off Featured Users
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Object Identity
How can we check if an object has a
getGravatar() method?
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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?
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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!
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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)
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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?
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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
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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());
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Exceptions
Exceptions are:
• beautiful errors
• objects
• opportunities
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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’
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Exceptions in PHP
We should catch exceptions:
1 try {
2 // success case code goes here
3 $db = new PDO("foo", "bar");
4 } catch(PDOException $e) {
5 echo "some DB fail occurred";
6 }
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Throwing Exceptions
function addTwoNumbers($a, $b) {
if(($a == 0) || ($b == 0)) {
throw new Exception("Zero is Boring!");
}
return $a + $b;
}
echo addTwoNumbers(3,2); // 5
echo addTwoNumbers(5,0); // error!!
Fatal error: Uncaught exception 'Exception'
with message 'Zero is Boring!'
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Extending Exceptions
We can extend the Exception class for our own
use
1 class DontBeDaftException extends Exception {
2 }
3
4 function inspectCurtains($colour) {
5 if($colour == "orange" || $colour == "spotty") {
6 throw new DontBeDaftException($colour . 'is daft');
7 }
8 echo "The curtains are $colour\n";
9 }
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And Breathe
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And Breathe
(just one more thing)
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Duplicate Functionality
Did you notice that the getGravatar() method is
identical in those unrelated classes?
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Traits
Traits are simply compiler-assisted copy/paste.
Rasmus Lerdorf
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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 "";
6 }
7 }
Good news: autoloading works for traits!
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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 ....
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Project Overview
.
├── inc
│ ├── Animal
│ │ └── Cat.php
│ ├── Gravatar.php
│ ├── Picturesque.php
│ └── User
│ ├── Admin.php
│ └── User.php
├── public
│ └── index.php
├── README.md
└── templates
└── ...
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That’s all, folks
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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
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Questions? (and resources)
Intermediate PHP http://lrnja.net/php-video
Contact me: @lornajane or http://lornajane.net
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