Online PHP editor | output for 7Z2Nt

<?php class ObjectNameGenerator { public function __invoke($object) { return $object->id; } } class b extends a { public function __construct() { parent::setCallableGenerator(new ObjectNameGenerator()); } } class a { private $callableGenerator = null; public function setCallableGenerator(callable $func) { $this->callableGenerator = $func; } public function build() { $object = new StdClass(); $object->id = 99; if($this->callableGenerator !== null) { return call_user_func($this->callableGenerator, $object); } else { return 'no callable function'; } } } $b = new b(); $b->build();