MultipleIterator::key Gets the registered iterator instances &reftitle.description; public arrayMultipleIterator::key Get the registered iterator instances key() result. &warn.undocumented.func; &reftitle.parameters; &no.function.parameters; &reftitle.returnvalues; An array of all registered iterator instances. &reftitle.errors; A RuntimeException if the iterator is invalid (as of PHP 8.1.0), or mode MIT_NEED_ALL is set, and at least one attached iterator is not valid. Calling this method from triggers warning "Illegal type returned". &reftitle.changelog; &Version; &Description; 8.1.0 A RuntimeException is now thrown if MultipleIterator::key is called on an invalid iterator. Previously, &false; was returned. &reftitle.seealso; MultipleIterator::current