PHP Singleton pattern example

UserSingleton.php

<?php

/** Example taken from http://www.webgeekly.com/tutorials/php/how-to-create-a-singleton-class-in-php/ **/

class User
{
    // Hold an instance of the class
    private static $instance;
 
    // The singleton method
    public static function singleton()
    {
        if (!isset(self::$instance)) {
            self::$instance = new __CLASS__;
        }
        return self::$instance;
    }
    
}

$user1 = User::singleton();
$user2 = User::singleton();
$user3 = User::singleton();


?>

CLASS should be new static()!

I use this trait

trait Singleton
{
    private static ?self $instance = null;

    final private function __construct()
    {
        // Singleton
    }

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

    final public function __clone()
    {
        throw new \LogicException('Clone is not allowed');
    }

    final public function __wakeup()
    {
        throw new \LogicException('Unserialization is not allowed');
    }
}

then

final class User
{
    use Singleton;
}

$user1 = User::getInstance();
$user2 = User::getInstance();
$user3 = User::getInstance();

• trait Singleton has only one responsibility: to be single
• class User has only one responsibility: to represent user
• everything is final because an extension from a singleton always gets an instance of the extended class