3.12. Template Method

3.12.1. Amaç

Alt sınıflar içerisinde kullanılabilecek yöntemleri üst sınıf içerisinde tanımlayarak, kopyala-yapıştır işlemini azaltıp, gereksiz kod yoğunluğunu önlemek.

Belki de bununla pek çok kez karşılamışsınızdır zaten. Aslında fikir, bu soyut şablonun alt sınıflarının bir algoritmanın davranışını “bitirmesini” sağlamaktır.

A.k.a the “Hollywood principle”: “Don’t call us, we call you.” This class is not called by subclasses but the inverse. How? With abstraction of course.

In other words, this is a skeleton of algorithm, well-suited for framework libraries. The user has just to implement one method and the superclass do the job.

Bu desenle somut sınıfların ayrışımı kolaylaşır ve kod bünyesindeki kopyala-yapıştır işlemi azalır. Bu yüzden bu desenle her yerde karşılaşabilirsiniz (örn. OppaAgentAgentCrud)).

3.12.2. UML Diyagramı

3.12.3. Kod

Bu kodu Github üzerinde de bulabilirsiniz.

Journey.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\TemplateMethod;

abstract class Journey
{
    /**
     * @var string[]
     */
    private array $thingsToDo = [];

    /**
     * This is the public service provided by this class and its subclasses.
     * Notice it is final to "freeze" the global behavior of algorithm.
     * If you want to override this contract, make an interface with only takeATrip()
     * and subclass it.
     */
    final public function takeATrip()
    {
        $this->thingsToDo[] = $this->buyAFlight();
        $this->thingsToDo[] = $this->takePlane();
        $this->thingsToDo[] = $this->enjoyVacation();
        $buyGift = $this->buyGift();

        if ($buyGift !== null) {
            $this->thingsToDo[] = $buyGift;
        }

        $this->thingsToDo[] = $this->takePlane();
    }

    /**
     * This method must be implemented, this is the key-feature of this pattern.
     */
    abstract protected function enjoyVacation(): string;

    /**
     * This method is also part of the algorithm but it is optional.
     * You can override it only if you need to
     */
    protected function buyGift(): ?string
    {
        return null;
    }

    private function buyAFlight(): string
    {
        return 'Buy a flight ticket';
    }

    private function takePlane(): string
    {
        return 'Taking the plane';
    }

    /**
     * @return string[]
     */
    final public function getThingsToDo(): array
    {
        return $this->thingsToDo;
    }
}

BeachJourney.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\TemplateMethod;

class BeachJourney extends Journey
{
    protected function enjoyVacation(): string
    {
        return "Swimming and sun-bathing";
    }
}

CityJourney.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\TemplateMethod;

class CityJourney extends Journey
{
    protected function enjoyVacation(): string
    {
        return "Eat, drink, take photos and sleep";
    }

    protected function buyGift(): ?string
    {
        return "Buy a gift";
    }
}

3.12.4. Test

Tests/JourneyTest.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\TemplateMethod\Tests;

use DesignPatterns\Behavioral\TemplateMethod\BeachJourney;
use DesignPatterns\Behavioral\TemplateMethod\CityJourney;
use PHPUnit\Framework\TestCase;

class JourneyTest extends TestCase
{
    public function testCanGetOnVacationOnTheBeach()
    {
        $beachJourney = new BeachJourney();
        $beachJourney->takeATrip();

        $this->assertSame(
            ['Buy a flight ticket', 'Taking the plane', 'Swimming and sun-bathing', 'Taking the plane'],
            $beachJourney->getThingsToDo()
        );
    }

    public function testCanGetOnAJourneyToACity()
    {
        $cityJourney = new CityJourney();
        $cityJourney->takeATrip();

        $this->assertSame(
            [
                'Buy a flight ticket',
                'Taking the plane',
                'Eat, drink, take photos and sleep',
                'Buy a gift',
                'Taking the plane'
            ],
            $cityJourney->getThingsToDo()
        );
    }
}