add example in case_when about consistent RHS (tidyverse#3247)

* add example in case_when about consistent RHS

* add dontrun example

* generation of Rd file

R/case_when.R

@@ -34,6 +34,31 @@
 #'   x %% 35 == 0 ~ "fizz buzz"
 #' )
 #'
+#' # All RHS needs to be the same type. Inconsitent types will throw an error.
+#' # This applies also to NA values used in RHS - NA is logical so you must use other
+#' # typed value like NA_real_, NA_complex, NA_character_, NA_integer_ in other cases
+#' case_when(
+#'   x %% 35 == 0 ~ NA_character_,
+#'   x %% 5 == 0 ~ "fizz",
+#'   x %% 7 == 0 ~ "buzz",
+#'   TRUE ~ as.character(x)
+#' )
+#' case_when(
+#'   x %% 35 == 0 ~ 35,
+#'   x %% 5 == 0 ~ 5,
+#'   x %% 7 == 0 ~ 7,
+#'   TRUE ~ NA_real_
+#' )
+#' # This throws an error as NA is logical not numeric
+#' \dontrun{
+#' case_when(
+#'   x %% 35 == 0 ~ 35,
+#'   x %% 5 == 0 ~ 5,
+#'   x %% 7 == 0 ~ 7,
+#'   TRUE ~ NA
+#' )
+#' }
+#'
 #' # case_when is particularly useful inside mutate when you want to
 #' # create a new variable that relies on a complex combination of existing
 #' # variables