Factory Design Pattern in PHP

Design patterns are essential in writing reusable, maintainable, and efficient code. The Factory Design Pattern is one of the creational patterns, used for creating objects without exposing the instantiation logic to the client. In this post, we will discuss the Factory Design Pattern in PHP 8.3, its benefits, and how to implement it effectively.

What is the Factory Design Pattern?

The Factory Pattern provides a way to delegate the instantiation of objects to a factory class, centralizing object creation logic. This pattern can help encapsulate the creation process, making it easier to introduce new object types or change instantiation details without modifying client code.

Imagine you have multiple classes with a common interface or base class and want to create instances of these classes based on some input or configuration. The Factory Pattern can simplify this process by defining a factory class responsible for creating and returning instances of these different classes.

When to Use the Factory Pattern?

Use the Factory Pattern when:

You have multiple classes that implement a common interface or share a base class.
You want to decouple client code from the specific classes it needs to instantiate.
You anticipate changes in the object instantiation logic in the future.

Implementing the Factory Design Pattern in PHP 8.3

Let’s consider a practical example where we have different types of notifications—like EmailNotification, SMSNotification, and PushNotification. All these notifications implement a common NotificationInterface.

Step 1: Define the Interface

The first step is to define the common interface that each notification type will implement:

<?php

interface NotificationInterface
{
    public function send(string $message): void;
}

Step 2: Create Concrete Classes

Each notification type should implement the NotificationInterface:

<?php

class EmailNotification implements NotificationInterface
{
    public function send(string $message): void
    {
        echo "Sending Email: $message\n";
    }
}

class SMSNotification implements NotificationInterface
{
    public function send(string $message): void
    {
        echo "Sending SMS: $message\n";
    }
}

class PushNotification implements NotificationInterface
{
    public function send(string $message): void
    {
        echo "Sending Push Notification: $message\n";
    }
}

Step 3: Create the Factory Class

Now, let’s create a NotificationFactory class that decides which notification instance to create based on a given type. PHP 8.3's match expression simplifies this conditional logic, making it more concise.

<?php

class NotificationFactory
{
    public static function create(string $type): NotificationInterface
    {
        return match ($type) {
            'email' => new EmailNotification(),
            'sms' => new SMSNotification(),
            'push' => new PushNotification(),
            default => throw new InvalidArgumentException("Invalid notification type: $type"),
        };
    }
}

In the factory class above, we use match to choose the appropriate notification class based on the $type parameter. If an invalid type is provided, we throw an InvalidArgumentException.

Step 4: Use the Factory to Create Instances

Now, we can use the NotificationFactory to create instances based on the type and use them without worrying about the instantiation details.

<?php

try {
    $notificationType = 'email'; // This could be dynamically determined in a real application
    $notification = NotificationFactory::create($notificationType);
    $notification->send("Hello from the Factory Pattern!");
} catch (InvalidArgumentException $e) {
    echo $e->getMessage();
}

In this example, if $notificationType is 'email', the factory will return an instance of EmailNotification. Then, we can call send() on the created notification.

Benefits of the Factory Pattern

Encapsulation of Object Creation: Clients do not need to know which specific class is being instantiated. This improves encapsulation and reduces coupling between classes.
Code Reusability: The factory class can be reused across the application wherever new objects of these types need to be created.
Simplified Code Maintenance: Changes to the object creation logic are centralized in the factory class, so they don’t impact client code.
Enhanced Flexibility: New types of notifications can be added without modifying existing client code.

Advanced Factory with Dependency Injection

In real-world applications, notifications might depend on external services (like a mail server or SMS gateway). In such cases, you can make the factory method more advanced by injecting dependencies.

For example, let’s inject a MailerService into the EmailNotification:

<?php

class MailerService
{
    public function sendMail(string $message): void
    {
        echo "Sending mail: $message\n";
    }
}

class EmailNotification implements NotificationInterface
{
    private MailerService $mailer;

    public function __construct(MailerService $mailer)
    {
        $this->mailer = $mailer;
    }

    public function send(string $message): void
    {
        $this->mailer->sendMail($message);
    }
}

Then, modify the NotificationFactory to inject this dependency:

<?php

class NotificationFactory
{
    private MailerService $mailer;

    public function __construct(MailerService $mailer)
    {
        $this->mailer = $mailer;
    }

    public function create(string $type): NotificationInterface
    {
        return match ($type) {
            'email' => new EmailNotification($this->mailer),
            'sms' => new SMSNotification(),
            'push' => new PushNotification(),
            default => throw new InvalidArgumentException("Invalid notification type: $type"),
        };
    }
}

Now, we instantiate NotificationFactory with the MailerService dependency:

<?php

$mailer = new MailerService();
$factory = new NotificationFactory($mailer);

$notification = $factory->create('email');
$notification->send("Hello with dependency injection!");

Conclusion

The Factory Design Pattern is a powerful tool in PHP that provides flexibility, modularity, and better code organization. PHP 8.3’s match expression further simplifies this pattern, making the factory code cleaner and more expressive.

By using this pattern, you can avoid tightly coupling your application to specific classes, improving the overall architecture. With the examples provided, you should now have a solid understanding of how to implement and extend the Factory Pattern in PHP 8.3 for creating versatile and maintainable applications.