Function nested_refs

cpp/src/arrow/type.h:2173–2177

    return IsName() ? &std::get<std::string>(impl_) : NULLPTR;
  }
  const std::vector<FieldRef>* nested_refs() const {
    return std::holds_alternative<std::vector<FieldRef>>(impl_)
               ? &std::get<std::vector<FieldRef>>(impl_)
               : NULLPTR;
  }

  /// \brief Retrieve FieldPath of every child field which matches this FieldRef.
  std::vector<FieldPath> FindAll(const Schema& schema) const;