Method erase_same_node

src/include/cpp-btree/btree.h:2109–2134

template <typename P>
void btree<P>::erase_same_node(iterator begin, iterator end) {
  assert(begin.node == end.node);
  assert(end.position > begin.position);

  node_type *node = begin.node;
  size_type to_erase = end.position - begin.position;
  if (!node->leaf()) {
    // Delete all children between begin and end.
    for (size_type i = 0; i < to_erase; ++i) {
      internal_clear(node->child(begin.position + i + 1));
    }
    // Rotate children after end into new positions.
    for (size_type i = begin.position + to_erase + 1; i <= node->count(); ++i) {
      node->set_child(i - to_erase, node->child(i));
      node->clear_child(i);
    }
  }
  node->remove_values_ignore_children(begin.position, to_erase,
                                      mutable_allocator());

  // Do not need to update rightmost_, because
  // * either end == this->end(), and therefore node == rightmost_, and still
  //   exists
  // * or end != this->end(), and therefore rightmost_ hasn't been erased, since
  //   it wasn't covered in [begin, end)
}

template <typename P>
auto btree<P>::erase_from_leaf_node(iterator begin, size_type to_erase)