Method Next

cpp/src/arrow/util/iterator.h:541–564

  explicit FlattenIterator(Iterator<Iterator<T>> it) : parent_(std::move(it)) {}

  Result<T> Next() {
    if (IsIterationEnd(child_)) {
      // Pop from parent's iterator.
      ARROW_ASSIGN_OR_RAISE(child_, parent_.Next());

      // Check if final iteration reached.
      if (IsIterationEnd(child_)) {
        return IterationTraits<T>::End();
      }

      return Next();
    }

    // Pop from child_ and check for depletion.
    ARROW_ASSIGN_OR_RAISE(T out, child_.Next());
    if (IsIterationEnd(out)) {
      // Reset state such that we pop from parent on the recursive call
      child_ = IterationTraits<Iterator<T>>::End();

      return Next();
    }

    return out;
  }

 private:
  Iterator<Iterator<T>> parent_;