$k]; yield [[1, 2 => 2, 4 => 3], [1, 2, 3], fn (int $k): int => $k * 2]; yield [['0' => 1, '1' => 2, '2' => 3], [1, 2, 3], fn (int $k): string => (string) $k]; yield [[], [], fn (int $k): string => (string) $k]; } }