目的

动态地为类的实例添加功能

例子

• Web Service层：REST服务的JSON与XML装饰器（当然，在此只能使用其中的一种）

UML 图

 代码

Booking.php

<?php

declare(strict_types=1);

namespace DesignPatternsStructuralDecorator;

interface Booking
{
    public function calculatePrice(): int;

    public function getDescription(): string;
}

BookingDecorator.php

<?php

declare(strict_types=1);

namespace DesignPatternsStructuralDecorator;

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

DoubleRoomBooking.php

<?php

declare(strict_types=1);

namespace DesignPatternsStructuralDecorator;

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

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

ExtraBed.php

<?php

declare(strict_types=1);

namespace DesignPatternsStructuralDecorator;

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

declare(strict_types=1);

namespace DesignPatternsStructuralDecorator;

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";
    }
}

测试

Tests/DecoratorTest.php

<?php

declare(strict_types=1);

namespace DesignPatternsStructuralDecoratorTests;

use DesignPatternsStructuralDecoratorDoubleRoomBooking;
use DesignPatternsStructuralDecoratorExtraBed;
use DesignPatternsStructuralDecoratorWiFi;
use PHPUnitFrameworkTestCase;

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());
    }
}