Function GetOne

cpp/src/arrow/type.h:2264–2267

  /// Emit an error if none or multiple match.
  template <typename T>
  Result<GetType<T>> GetOne(const T& root) const {
    ARROW_ASSIGN_OR_RAISE(auto match, FindOne(root));
    return match.Get(root).ValueOrDie();
  }
  /// \brief Get the single child matching this FieldRef.
  ///
  /// Unlike `FieldRef::GetOne`, this variant is not zero-copy and the retrieved