Creating the Singleton design pattern in PHP5

Question

How would one create a Singleton class using PHP5 classes?

Answer 1

protected  static $_instance;

public static function getInstance()
{
    if(is_null(self::$_instance))
    {
        self::$_instance = new self();
    }
    return self::$_instance;
}

This code can apply for any class without caring about its class name.