Method dictionary

cpp/src/arrow/compute/kernels/vector_hash.cc:508–520

This can't be called more than once because DictionaryUnifier::GetResult() can't be called more than once and produce the same output.

  /// This can't be called more than once because DictionaryUnifier::GetResult()
  /// can't be called more than once and produce the same output.
  Result<std::shared_ptr<Array>> dictionary() const {
    if (!first_dictionary_) {  // Append was never called
      return nullptr;
    }
    if (!dictionary_unifier_) {  // Append was called only once
      return first_dictionary_;
    }

    auto out_dict_type = first_dictionary_->type();
    std::shared_ptr<Array> out_dict;
    RETURN_NOT_OK(dictionary_unifier_->GetResult(&out_dict_type, &out_dict));
    return out_dict;
  }

 private:
  std::unique_ptr<HashKernel> indices_kernel_;