UberSingleton.php

<?php

class UberSingleton {
    
    private $state = 0;
    
    private static $instance;
    
    private function __construct() {}
    
    public static function getInstance() {
        if (self::$instance === null) {
            self::$instance = new self;
        }
        return self::$instance;
    }
    
    public function __clone() {
        throw new Exception("Singleton!");
    }
    
    public function __sleep() {
        throw new Exception("Singleton²!");
    }
    
    public function doSomething() {
        $this->state++;
    }
    
    public function __toString() {
        return "Singleton: " . $this->state . "<br />";
    }
}

//$obj = new UberSingleton(); // Fatal error: Call to private UberSingleton::__construct() from invalid context
$obj = UberSingleton::getInstance();
//$otherObj = clone $obj; // Fatal error: Uncaught exception 'Exception' with message 'Singleton!'
//$serialized = serialize($obj); // Fatal error: Uncaught exception 'Exception' with message 'Singleton²!'