2.5. Decorator

2.5.1. Purpose

To dynamically add new functionality to class instances.

2.5.2. Examples

• Zend Framework: decorators for Zend_Form_Element instances
• Web Service Layer: Decorators JSON and XML for a REST service (inthis case, only one of these should be allowed of course)

2.5.3. UML Diagram

2.5.4. Code

You can also find this code on GitHub

Booking.php

<?php
 
namespace DesignPatterns\Structural\Decorator;
 
interface Booking
{
    public function calculatePrice(): int;
 
    public function getDescription(): string;
}

BookingDecorator.php

<?php
 
namespace DesignPatterns\Structural\Decorator;
 
abstract class BookingDecorator implements Booking
{
    /**
     * @var Booking
     */
    protected $booking;
 
    public function __construct(Booking $booking)
    {
        $this->booking = $booking;
    }
}

DoubleRoomBooking.php

<?php
 
namespace DesignPatterns\Structural\Decorator;
 
class DoubleRoomBooking implements Booking
{
    public function calculatePrice(): int
    {
        return 40;
    }
 
    public function getDescription(): string
    {
        return 'double room';
    }
}

ExtraBed.php

<?php
 
namespace DesignPatterns\Structural\Decorator;
 
class ExtraBed extends BookingDecorator
{
    private const PRICE = 30;
 
    public function calculatePrice(): int
    {
        return $this->booking->calculatePrice() + self::PRICE;
    }
 
    public function getDescription(): string
    {
        return $this->booking->getDescription() . ' with extra bed';
    }
}

WiFi.php

<?php
 
namespace DesignPatterns\Structural\Decorator;
 
class WiFi extends BookingDecorator
{
    private const PRICE = 2;
 
    public function calculatePrice(): int
    {
        return $this->booking->calculatePrice() + self::PRICE;
    }
 
    public function getDescription(): string
    {
        return $this->booking->getDescription() . ' with wifi';
    }
}

2.5.5. Test

Tests/DecoratorTest.php

<?php
 
namespace DesignPatterns\Structural\Decorator\Tests;
 
use DesignPatterns\Structural\Decorator\DoubleRoomBooking;
use DesignPatterns\Structural\Decorator\ExtraBed;
use DesignPatterns\Structural\Decorator\WiFi;
use PHPUnit\Framework\TestCase;
 
class DecoratorTest extends TestCase
{
    public function testCanCalculatePriceForBasicDoubleRoomBooking()
    {
        $booking = new DoubleRoomBooking();
 
        $this->assertEquals(40, $booking->calculatePrice());
        $this->assertEquals('double room', $booking->getDescription());
    }
 
    public function testCanCalculatePriceForDoubleRoomBookingWithWiFi()
    {
        $booking = new DoubleRoomBooking();
        $booking = new WiFi($booking);
 
        $this->assertEquals(42, $booking->calculatePrice());
        $this->assertEquals('double room with wifi', $booking->getDescription());
    }
 
    public function testCanCalculatePriceForDoubleRoomBookingWithWiFiAndExtraBed()
    {
        $booking = new DoubleRoomBooking();
        $booking = new WiFi($booking);
        $booking = new ExtraBed($booking);
 
        $this->assertEquals(72, $booking->calculatePrice());
        $this->assertEquals('double room with wifi with extra bed', $booking->getDescription());
    }
}