Function GetOneOrNone

cpp/src/arrow/type.h:2281–2287

  /// Return nullptr if none match, emit an error if multiple match.
  template <typename T>
  Result<GetType<T>> GetOneOrNone(const T& root) const {
    ARROW_ASSIGN_OR_RAISE(auto match, FindOneOrNone(root));
    if (match.empty()) {
      return static_cast<GetType<T>>(NULLPTR);
    }
    return match.Get(root).ValueOrDie();
  }
  /// \brief Get the single child matching this FieldRef.
  ///
  /// Return nullptr if none match, emit an error if multiple match.