单例模式-创建型设计模式 [PHP]

final class Singleton{\n    private static ?Singleton $instance = null;\n    public static function getInstance(): Singleton\n    {\n        if (static::$instance === null) {\n            static::$instance = new static();\n        }\n        return static::$instance;\n    }\n    private function __construct(){\n    }\n    private function __clone(){\n    }\n    private function __wakeup(){\n    }\n}