class Singleton { private static $instance = null; private function __construct() { } public static function getInstance() { if (self::$instance == null) { self::$instance = new Singleton; } return self::$instance; } }In this example, a private static instance variable is declared as null. The constructor method is private, so the class cannot be instantiated from outside of the class. Instead, the getInstance method is used to access the single instance of the class. The getInstance method checks if the instance variable is null. If it is, it creates a new instance of the class and assigns it to the instance variable. The method then returns the instance variable. This method can be used in a variety of contexts, such as creating a database connection or managing user sessions. The package library for this method would depend on the context in which it is being used. If it is being used in a PHP framework like Laravel, it would be part of the framework's core libraries. If it is being used in a custom PHP application, it would be included in the application's codebase.