a SingletonSample instance was created !
instance ID : d4e24632fab1e31460611f60b1a0b69c
$instance1->getId() === $instance2->getId() : ture

Fatal error: Uncaught RuntimeException: Clone is not allowed againstSingletonSample in /var/www/vhosts/www.yuulinux.tokyo/httpdocs/demo/Design-Pattern-Primer-by-PHP/Singleton/SingletonSample.class.php:58 Stack trace: #0 /var/www/vhosts/www.yuulinux.tokyo/httpdocs/demo/Design-Pattern-Primer-by-PHP/Singleton/index.php(27): SingletonSample->__clone() #1 {main} thrown in /var/www/vhosts/www.yuulinux.tokyo/httpdocs/demo/Design-Pattern-Primer-by-PHP/Singleton/SingletonSample.class.php on line 58