php-src/ext/opcache/tests/preload_bug78175_2.inc

<?php
class Loader {
    static private $loader;

    static function getLoader() {
        if (null !== self::$loader) {
            return self::$loader;
        }
        return self::$loader = new Loader();
    }

    static function getCounter() {
        static $counter = 0;
        return $counter++;
    }
}

class ExtLoader extends Loader {
}

Loader::getLoader();
Loader::getCounter();
Loader::getCounter();