@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 Tree<T> clear() {
return Tree.empty();
}
/**
* Returns a Tree containing {@code n} values supplied by a given Supplier {@code s}.
*
* @param <T> Component type of the Tree
* @param n The number of elements in the Tree
* @param s The Supplier computing element values
* @return A Tree of size {@code n}, where each element contains the result supplied by {@code s}.
* @throws NullPointerException if {@code s} is null
*/
static <T> Tree<T> fill(int n, Supplier<? extends T> s) {
Objects.requireNonNull(s, "s is null");
return Collections.fill(n, s, Tree.empty(), Tree::of);
}
/**
* Returns a Tree containing {@code n} values of a given Function {@code f} over a range of
* integer values from 0 to {@code n - 1}.
*
* @param <T> Component type of the Tree
* @param n The number of elements in the Tree
* @param f The Function computing element values
* @return A Tree consisting of elements {@code f(0),f(1), ..., f(n - 1)}
* @throws NullPointerException if {@code f} is null
*/
static <T> Tree<T> tabulate(int n, Function<? super Integer, ? extends T> f) {
Objects.requireNonNull(f, "f is null");
return Collections.tabulate(n, f, Tree.empty(), Tree::of);
}