public <V> Object[] build(Iterable<V> source, UpdateFunction<V> updateF, int size) {
assert updateF != null;
NodeBuilder current = rootBuilder;
// we descend only to avoid wasting memory; in update() we will often descend into existing
// trees
// so here we want to descend also, so we don't have lg max(N) depth in both directions
while ((size >>= FAN_SHIFT) > 0) current = current.ensureChild();
current.reset(EMPTY_LEAF, POSITIVE_INFINITY, updateF, null);
for (V key : source) current.addNewKey(key);
current = current.ascendToRoot();
Object[] r = current.toNode();
current.clear();
return r;
}
