Fellipe Sanches' website

Category: Design Pattern

  • Factory Method

    Factory Method

    Factory method provides an interface for creating objects in a superclass,
    allows subclasses to decide wich class to instantiate.

    //Concrete or direct instantiation. Client code with no factory.
$myEmailNotification = new emailNotification;
$mySmsNotification = new smsNotification;

//Abstracted object creation. Client code with a factory-based instantiation.
$myEmailNotification = NotificationFactory::create('email');
$mySmsNotification = NotificationFactory::create('sms');

    Factories allow client code to operate on generalizations, this is called coding to an interface, not an implementation and is a fundamental principle in object-oriented programming that promotes flexibility, maintainability, and testability in software design. 

    It means that client code should interact with a system through an abstract interface (or abstract class) rather than create the object directly, without worrying about the details of object creation. 

    <?php
// interface defines a contract — all notification classes must have a send() method.
interface Notification
{
    public function send(string $to, string $message): void;
}

// Concrete implementations of different notification types

class EmailNotification implements Notification
{
    public function send(string $to, string $message): void
    {
        echo "Sending EMAIL to {$to}: {$message}" . PHP_EOL;
    }
}

class SmsNotification implements Notification
{
    public function send(string $to, string $message): void
    {
        echo "Sending SMS to {$to}: {$message}" . PHP_EOL;
    }
}

class PushNotification implements Notification
{
    public function send(string $to, string $message): void
    {
        echo "Sending PUSH notification to {$to}: {$message}" . PHP_EOL;
    }
}

// The Factory class — decides which notification to create
class NotificationFactory
{
    public static function create(string $type): Notification
    {
        return match (strtolower($type)) {
            'email' => new EmailNotification(),
            'sms'   => new SmsNotification(),
            'push'  => new PushNotification(),
            default => throw new InvalidArgumentException("Unknown notification type: {$type}")
        };
    }
}

// Usage exemple
try {
    $notification = NotificationFactory::create('email');
    $notification->send('user@example.com', 'Your order has been shipped.');

    $notification = NotificationFactory::create('sms');
    $notification->send('+5547999999999', 'Your code is 123456.');

    $notification = NotificationFactory::create('push');
    $notification->send('User123', 'You have a new message.');
} catch (Exception $e) {
    echo "Error: " . $e->getMessage();
}

  • Singleton

    Singleton

    Singleton – ensure that a class has only one instance,
    while providing a global access point to this instance

    <?php

class Logger
{
    private static ?Logger $uniqueInstance = null;
    private array $logs = [];

    // prevents direct instantiation
    private function __construct() {}

    // no one outside the class can duplicate the instance.
    private function __clone() {}

    /* __wakeup must be public (by PHP’s design), 
    since it’s automatically called during unserialize().*/
    public function __wakeup()
    {
        throw new \Exception("Cannot unserialize a singleton.");
    }

    /* Lazy construction / initialization - returns the single instance 
    of this class*/
    public static function getInstance(): Logger
    {
        if (self::$uniqueInstance === null) {
            self::$uniqueInstance = new Logger();
        }
        return self::$uniqueInstance;
    }

    // Methods
    public function addLog(string $message): void
    {
        $this->logs[] = $message;
    }

    public function showLogs(): void
    {
        foreach ($this->logs as $log) {
            echo $log . PHP_EOL;
        }
    }
}

// Usage exemple
$logger1 = Logger::getInstance();
$logger2 = Logger::getInstance();

$logger1->addLog("First log entry.");
$logger2->addLog("Second log entry.");

$logger1->showLogs();

//Checking the solid proof...

if ($logger1 === $logger2) {
    echo "Same instance" . PHP_EOL;
} else {
    echo "Different instances" . PHP_EOL;
}

echo "Logger1 ID: " . spl_object_id($logger1) . PHP_EOL;
echo "Logger2 ID: " . spl_object_id($logger2) . PHP_EOL;

/*
Output:

First log entry.
Second log entry.
Same instance
Logger1 ID: 1
Logger2 ID: 1
*/

    The code above works perfectly for our purpose, but it’s not inheritance-safe, meaning it always creates a Logger instance, even if called from a subclass. Therefore:

    class FileLogger extends Logger {}
FileLogger::getInstance(); //still returns the instance of Logger, not a instance of FileLogger

    If we want that each subclass has its own singleton, we must change this behavior by modifying the getInstance() method, like this:

    public static function getInstance(): Logger 
{
    $className = static::class;
    if (!isset(self::$uniqueInstance[$className])) {
        self::$uniqueInstance[$className] = new static();
    }
    return self::$uniqueInstance[$className];
}

    Comparison:

    FeatureVersion
    self    		Version
    static::class
    Supports inheritance❌ No✅ Yes
    Each subclass has its own singleton❌ No✅ Yes
    Refers to who?Refer to the class where the code was originally defined.Refer to the class that was actually called at runtime.
    When use?You want a single, strict singleton for only the original class.You expect inheritance or extensions of your original class.

    When Singleton pattern is useful?

    • Logger – Keep a single instance that writes all logs from different parts of the app.
    • Configuration Manager – Store settings (like API keys, database credentials, etc.) in one place.
    • Database Connection – Maintain one connection to the database.
    • Cache Manager – Keep a single cache handler (like Redis, Memcached, or file cache)
    • Session Manager – Handle user session data globally.
    • Event Dispatcher or Queue Manager – Centralize how events or background tasks are managed.