type-> class

Author: venom1204

NEWS.md

@@ -107,6 +107,8 @@
 
 18. `fwrite` now allows `dec` to be the same as `sep` for edge cases where only one will be written, e.g. 0-row or 1-column tables. [#7227](https://github.com/Rdatatable/data.table/issues/7227). Thanks @MichaelChirico for the report and @venom1204 for the fix.
 
+19. `rowwiseDT()` now provides a helpful error message when a complex object that is not a list (e.g., a function) is provided as a cell value, instructing the user to wrap it in `list()`. [#7219](https://github.com/Rdatatable/data.table/issues/7219). Thanks @kylebutts for the report and @venom1204 for the fix.
+
 ### NOTES
 
 1. The following in-progress deprecations have proceeded:

R/rowwiseDT.R

@@ -21,9 +21,9 @@ rowwiseDT = function(...) {
     first_problem_idx = which(is_problematic)[1L]
     col_idx = (first_problem_idx - 1L) %% ncols + 1L
     col_name = header[col_idx]
-    obj_type = typeof(body[[first_problem_idx]])
+    obj_type = class(body[[first_problem_idx]])[1L]
     stopf(
-      "In column '%s', received an object of type '%s'.\nComplex objects (like functions, models, etc.) must be wrapped in list() to be stored in a data.table column.\nPlease use `list(...)` for this value.",
+      "In column '%s', received an object of type '%s'.\nComplex objects (like functions, formulas, or calls) must be wrapped in list() to be stored in a data.table column.\nPlease use `list(...)` for this value.",
       col_name,
       obj_type
     )