@SuppressWarnings("unchecked")
static <T, U> Tree<U> apply(
Node<T> node, Function<? super T, ? extends Iterable<? extends U>> mapper) {
final Tree<U> mapped = Tree.ofAll(mapper.apply(node.getValue()));
if (mapped.isEmpty()) {
return Tree.empty();
} else {
final List<Node<U>> children =
(List<Node<U>>)
(Object)
node.getChildren()
.map(child -> FlatMap.apply(child, mapper))
.filter(Tree::isDefined);
return Tree.of(mapped.getValue(), children.prependAll(mapped.getChildren()));
}
}
@Override
default <U> Tree<U> flatMap(Function<? super T, ? extends Iterable<? extends U>> mapper) {
Objects.requireNonNull(mapper, "mapper is null");
return isEmpty() ? Empty.instance() : FlatMap.apply((Node<T>) this, mapper);
}