Since PHP 5.5.X foreach can accept non scalar items. So the return can be anything ;)
(PHP 5, PHP 7, PHP 8)
Iterator::key — Retourne la clé de l'élément courant
Cette fonction ne contient aucun paramètre.
Retourne un scalaire en cas de succès, ou
null si une erreur survient.
Émet une alerte de type E_NOTICE si une erreur survient.
Since PHP 5.5.X foreach can accept non scalar items. So the return can be anything ;)And converts everything to integer except string, so in php the post process could be: public function key() { $yourKey = $this->createYourKey(); if (is_object($yourKey) || is_array($yourKey)) throw new Exception('Array and Object not allowed.'); elseif (is_string($yourKey)) return $yourKey; else return (int) $yourKey; }This function may return any type, not just scalar, for some Iterator types. In particular, it is very trivial to write a generator function that yields arbitrary keys:<?phpfunction foo() { yield null => 1; yield new stdclass => 2;}?>