sclass CloseableMapI<A, B> extends CloseableItIt<B> {
  IF1<A, B> f;
  Iterator<A> it;
  
  *(IF1<A, B> *f, Iterator<A> *it) {}
  
  public bool hasNext() {
    ret it.hasNext();
  }
  
  public B next() {
    ret f.get(it.next());
  }
  
  close {
    if (it cast AutoCloseable) {
      it.close();
      it = null;
    }
  }
}

Began life as a copy of #1035103