An Introduction to Object-Oriented Programming (DrupalCamp Leuven 2015)

AN INTRODUCTION TO
OBJECT-ORIENTED
PROGRAMMING (OOP)
I am , , and .Xano @BartFeenstra http://mynameisbart.com

WHAT IS OBJECT-ORIENTED
PROGRAMMING?
The form of programming that uses instances (objects) of classes
(predefined data types) to structure (group) information and functionality.

GLOSSARY
Class
A predefined type (blueprint) of complex data.
Object
An instance of a class; a single unit of complex data.
Property
A variable that belongs to a class or object.
Method
A function that belongs to a class or object.

STATE
Objects have state (internal configuration) which can be changed.
Most, if not all usages of static variables in Drupal 7 have been replaced with
object properties in Drupal 8.

INTERFACES
Interfaces define what objects must be able to do,
but do not define how they must do these things.
They are contracts that must be fulfilled.
<?php
interface FooInterface {
public function doFoo($foo);
}
interface FooMultipleInterface extends FooInterface {
public function doFooMultiple(array $foos);
}

CLASSES
Classes define what objects must do and how to do this.
In good design, they implement interfaces.
Classes can be instantiated into objects.
<?php
class Foo implements FooInterface {
public function doFoo($foo) {
return sprintf('Hello %s!', $foo);
}
}
$foo = new Foo();
$foo->doFoo('world');
// returns "Hello world!"

ABSTRACT CLASSES
Abstract classes provide partial implementations, but cannot be
instantiated.
<?php
abstract class AbstractFoo implements FooMultipleInterface {
}
}
class Foo extends AbstractFoo implements FooMultipleInterface {
public function doFooMultiple(array $foos) {
$greetings = [];
foreach ($foos as $foo) {
$greetings[] = sprintf('Hello %s!', $foo);
}
return implode(' ', $greetings);
}
}

TRAITS
Traits provide re-usable implementations that can reduce boilerplate code.
Classes can use traits.
<?php
trait FooTrait {
}
}
use FooTrait;
}
$foo = new Foo();
$foo->doFoo('world');
// returns "Hello world!"

INHERITANCE
Interfaces, traits, and classes can be extended.
Child classes can access methods from their parent classes.
<?php
}
}
class PoliteFoo extends Foo {
$message = parent::doFoo($foo);
$message .= ' How are you?';
return $message;
}
}

$THIS
$this points to the current object.
<?php
abstract class AbstractFoo implements FooMultipleInterface {
}
}
class Foo extends AbstractFoo implements FooMultipleInterface {
public function doFooMultiple(array $foos) {
$greetings = [];
foreach ($foos as $foo) {
$greetings[] = $this->doFoo($foo);
}
return implode(' ', $greetings);
}
}

VISIBILITY
Developers control which methods can be called from outside the class.
public
Can be called from anywhere.
protected
Can be called only from within the class or any child class.
private
Can only be called from within the same class.
<?php
class Bar {
protected function doBar() {}
}
$bar = new Bar();
$bar->doBar();
// $bar->doBar() causes an error, because we call a protected method from outside the class.

CHECKING AN OBJECT'S TYPE
When accepted as a function parameter (type hinting).
In a block of code (instanceof).
<?php
function foo(FooInterface $foo) {
// Here we only know $foo implements FooInterface.
if ($foo instanceof FooMultipleInterface) {
// Now we know $foo implements FooMultipleInterface too.
}
}

AUTOLOADING USING PSR-4
Industry standard with several available autoloaders.
Class names map to file names.
Namespaces map to directory names.
Much faster and less frustrating than the Drupal 7 registry.
Example: DrupalpaymentEntityPaymentInterfacemaps to
./src/Entity/PaymentInterface.php.

BENEFITS
Classes objects are faster than arrays
( ).
Interfaces and classes are documentation.
IDEs use interfaces and classes for code completion.
Easier and faster coding. Lower chance of bugs.
https://gist.github.com/nikic/5015323

CONCLUSION
OOP MAKES YOU A BETTER DEVELOPER.
Review this presentation at .http://slideshare.net/bartfeenstra
I am , , and .Xano @BartFeenstra http://mynameisbart.com
DO YOU HAVE ANY QUESTIONS?

An Introduction to Object-Oriented Programming (DrupalCamp Leuven 2015)

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