https://ievetrov.ru/kotlin-%d1%81-%d0%bd%d1%83%d0%bb%d1%8f-%d1%83%d1%80%d0%be%d0%ba%d0%b8/%d1%83%d1%80%d0%be%d0%ba-17-%d1%81%d0%b5%d1%82%d1%82%d0%b5%d1%80%d1%8b-%d0%b8-%d0%b3%d0%b5%d1%82%d1%82%d0%b5%d1%80%d1%8b/