Singleton pattern in PHP

What is the Singleton pattern

The Singleton pattern ensures that a class has only one instance and provides a global point of access to that instance.

Why we use it

1. Single Instance: Ensures that a class has only one instance, which is useful in scenarios where a single point of control or coordination is required.
2. Global Access: Provides a global point of access to the instance, making it easy to access and manage from anywhere in the codebase.
3. Lazy Initialization: The instance is created only when it is first needed, improving performance by avoiding unnecessary instantiation.

How Use it

Example :

we'll use a DatabaseConnection class as a Singleton website to manage a single database connection throughout the website

class DatabaseConnection {
    private static $instance;
    private $connection;

    private function __construct() {
        // database connection
        $this->connection = new PDO('mysql:host=localhost;dbname=mydatabase', 'username', 'password');
    }

    public static function getInstance() {
        if (null === self::$instance) {
            self::$instance = new self();
        }

        return self::$instance;
    }

    public function getConnection() {
        return $this->connection;
    }
}

// Example usage in a web pages: 

$database = DatabaseConnection::getInstance();
$connection = $database->getConnection();

// Now you can use $connection to perform database queries throughout your webpage
// without establishing a new connection every time.        

Another example we can use for session management in website

class AuthManager {
    public static function login($username, $password) {
        // authentication logic, check credentials against a database
        if ($username === 'demo' && $password === 'password') {
            $_SESSION['user'] = $username;
            return true;
        }
        return false;
    }

    public static function logout() {
        // Perform logout logic, destroy the session
        session_destroy();
    }

    public static function isAuthenticated() {
        // Check if a user is authenticated
        return isset($_SESSION['user']);
    }

    public static function getCurrentUser() {
        // Get the current user from the session
        return $_SESSION['user'] ?? null;
    }
}

// Usage example in web pages:

session_start();

// Perform login
AuthManager::login('demo', 'password');

// Check authentication status
if (AuthManager::isAuthenticated()) {
    echo "Welcome, " . AuthManager::getCurrentUser();
} else {
    echo "Not authenticated. Redirect to login page.";
}
        

above example are simple.