message: Define slots for strings used
diff: @@ -70,11 +70,27 @@ struct DataFrameScanFunction : public TableFunction {
  };
  struct RStrings {
  - SEXP secs;
  + SEXP secs; // Rf_mkChar
  SEXP mins;
  SEXP hours;
  SEXP days;
  SEXP weeks;
  + SEXP POSIXct;
  + SEXP POSIXt;
  + SEXP UTC_str; // Rf_mkString
  + SEXP Date_str;
  + SEXP difftime_str;
  + SEXP arrow_str; // StringsToSexp
  + SEXP POSIXct_POSIXt_str;
  + SEXP str_ref_type_names_rtypes_n_param_str; // StringsToSexp
  + SEXP _registered_df__sym; // Rf_install
  + SEXP _registered_arrow__sym;
  + SEXP tzone_sym;
  + SEXP units_sym;
  + SEXP getNamespace_sym;
  + SEXP ImportSchema_sym;
  + SEXP ImportRecordBatch_sym;
  + SEXP ImportRecordBatchReader_sym;
  static const RStrings &get() {
  // On demand
  