flatMap

inline fun <T, R> Iterable<T>.flatMap(transform: (T) -> Array<R>): List<R>
inline fun <K, V, R> Map<K, V>.flatMap(transform: (Map.Entry<K, V>) -> Array<R>): List<R>
fun <T, R> Sequence<T>.flatMap(transform: (T) -> Array<R>): Sequence<R>