Method AppendNull

cpp/src/arrow/json/parser.cc:532–583

Appending null is slightly tricky since null count is stored inline for builders of Kind::kNull. Append nulls using this helper

  /// Appending null is slightly tricky since null count is stored inline
  /// for builders of Kind::kNull. Append nulls using this helper
  Status AppendNull(BuilderPtr parent, int field_index, BuilderPtr builder) {
    if (ARROW_PREDICT_FALSE(!builder.nullable)) {
      return ParseError("a required field was null");
    }
    switch (builder.kind) {
      case Kind::kNull: {
        DCHECK_EQ(builder, parent.kind == Kind::kArray
                               ? Cast<Kind::kArray>(parent)->value_builder()
                               : Cast<Kind::kObject>(parent)->field_builder(field_index));

        // increment null count stored inline
        builder.index += 1;

        // update the parent, since changing builder doesn't affect parent
        if (parent.kind == Kind::kArray) {
          Cast<Kind::kArray>(parent)->value_builder(builder);
        } else {
          Cast<Kind::kObject>(parent)->field_builder(field_index, builder);
        }
        return Status::OK();
      }
      case Kind::kBoolean:
        return Cast<Kind::kBoolean>(builder)->AppendNull();

      case Kind::kNumber:
        return Cast<Kind::kNumber>(builder)->AppendNull();

      case Kind::kString:
        return Cast<Kind::kString>(builder)->AppendNull();

      case Kind::kNumberOrString: {
        return Cast<Kind::kNumberOrString>(builder)->AppendNull();
      }

      case Kind::kArray:
        return Cast<Kind::kArray>(builder)->AppendNull();

      case Kind::kObject: {
        auto struct_builder = Cast<Kind::kObject>(builder);
        RETURN_NOT_OK(struct_builder->AppendNull());

        for (int i = 0; i < struct_builder->num_fields(); ++i) {
          auto field_builder = struct_builder->field_builder(i);
          RETURN_NOT_OK(AppendNull(builder, i, field_builder));
        }
        return Status::OK();
      }

      default:
        return Status::NotImplemented("invalid builder Kind");
    }
  }

  Status Finish(const std::shared_ptr<Array>& scalar_values, BuilderPtr builder,
                std::shared_ptr<Array>* out) {