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run code in 500+ PHP versions simultaneously
<?php class A { private static self $singleton; public function __construct() { if(!isset(self::$singleton)) { self::$singleton = $this; } return self::$singleton; } } $a = new A; $b = new A; $c = new A; var_dump($a); var_dump($b); var_dump($c);

preferences:
86.98 ms | 1257 KiB | 5 Q