Method Extend

r/src/r_to_arrow.cpp:1069–1090

class RListConverter : public ListConverter<T, RConverter, RConverterTrait> {
 public:
  Status Extend(SEXP x, int64_t size, int64_t offset = 0) override {
    RETURN_NOT_OK(this->Reserve(size));

    RVectorType rtype = GetVectorType(x);
    if (rtype != LIST) {
      return Status::Invalid("Cannot convert to list type");
    }

    auto append_null = [this]() { return this->list_builder_->AppendNull(); };

    auto append_value = [this](SEXP value) {
      // TODO: if we decide that this can be run concurrently
      //       we'll have to do vec_size() upfront
      R_xlen_t n = arrow::r::vec_size(value);

      RETURN_NOT_OK(this->list_builder_->ValidateOverflow(n));
      RETURN_NOT_OK(this->list_builder_->Append());
      return this->value_converter_.get()->Extend(value, n);
    };

    return VisitVector(RVectorIterator<SEXP>(x, offset), size, append_null, append_value);
  }

  void DelayedExtend(SEXP values, int64_t size, RTasks& tasks) override {
    // NOTE: because Extend::[]append_value() calls Extend() on the