2.5. Dekorator (Decorator)

2.5.1. Przeznaczenie

Pozwala na dynamiczne dodawanie nowych funkcji do istniejących klas podczas działania programu.

2.5.2. Przykłady

  • Web Service Layer: Dekorator typu JSON i XML używany w usłudze typu REST (w tym przykładzie tylko jeden z nich powinien być dozwolony).

2.5.3. Diagram UML

Alt Decorator UML Diagram

2.5.4. Kod

Ten kod znajdziesz również na GitHub.

Booking.php

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<?php

declare(strict_types=1);

namespace DesignPatterns\Structural\Decorator;

interface Booking
{
    public function calculatePrice(): int;

    public function getDescription(): string;
}

BookingDecorator.php

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<?php

declare(strict_types=1);

namespace DesignPatterns\Structural\Decorator;

abstract class BookingDecorator implements Booking
{
    public function __construct(protected Booking $booking)
    {
    }
}

DoubleRoomBooking.php

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<?php

declare(strict_types=1);

namespace DesignPatterns\Structural\Decorator;

class DoubleRoomBooking implements Booking
{
    public function calculatePrice(): int
    {
        return 40;
    }

    public function getDescription(): string
    {
        return 'double room';
    }
}

ExtraBed.php

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<?php

declare(strict_types=1);

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

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<?php

declare(strict_types=1);

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. Testy

Tests/DecoratorTest.php

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<?php

declare(strict_types=1);

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->assertSame(40, $booking->calculatePrice());
        $this->assertSame('double room', $booking->getDescription());
    }

    public function testCanCalculatePriceForDoubleRoomBookingWithWiFi()
    {
        $booking = new DoubleRoomBooking();
        $booking = new WiFi($booking);

        $this->assertSame(42, $booking->calculatePrice());
        $this->assertSame('double room with wifi', $booking->getDescription());
    }

    public function testCanCalculatePriceForDoubleRoomBookingWithWiFiAndExtraBed()
    {
        $booking = new DoubleRoomBooking();
        $booking = new WiFi($booking);
        $booking = new ExtraBed($booking);

        $this->assertSame(72, $booking->calculatePrice());
        $this->assertSame('double room with wifi with extra bed', $booking->getDescription());
    }
}