Method iterator_at

external/parallel_hashmap/phmap.h:3858–3861

    }

    iterator iterator_at(Inner *inner, 
                         const EmbeddedIterator& it) { 
        return {inner, &sets_[0] + num_tables, it}; 
    }
    const_iterator iterator_at(Inner *inner, 
                               const EmbeddedIterator& it) const { 
        return {inner, &sets_[0] + num_tables, it};