nealrichardson commented on code in PR #12817:
URL: https://github.com/apache/arrow/pull/12817#discussion_r852398025
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r/R/type.R:
##########
@@ -68,17 +69,50 @@ FLOAT_TYPES <- c("float16", "float32", "float64",
"halffloat", "float", "double"
#' type(c("A", "B", "C"))
#' type(mtcars)
#' type(Sys.Date())
+#' type(as.POSIXlt(Sys.Date()))
+#' type(vctrs::new_vctr(1:5, class = "my_custom_vctr_class"))
#' @export
-type <- function(x) UseMethod("type")
+type <- function(x) infer_type(x)
+#' @rdname type
#' @export
-type.default <- function(x) Array__infer_type(x)
+infer_type <- function(x, ...) UseMethod("infer_type")
#' @export
-type.ArrowDatum <- function(x) x$type
+infer_type.default <- function(x, ..., from_array_infer_type = FALSE) {
+ # If from_array_infer_type is TRUE, this is a call from C++ and there was
+ # no S3 method defined for this object.
+ if (from_array_infer_type) {
+ abort(
+ sprintf(
+ "Can't infer Arrow data type from object inheriting from %s",
+ paste(class(x), collapse = " / ")
+ )
+ )
+ }
+
+ # If from_array_infer_type is FALSE, this is a user calling type() from R
+ # and we to call into C++. If there is no built-in conversion for this
+ # object type, C++ will call back here with from_array_infer_type = TRUE
+ # to generate a nice error message.
+ Array__infer_type(x)
+}
+
+#' @export
+infer_type.ArrowDatum <- function(x, ...) x$type
Review Comment:
This isn't an inference though. (Not a reason not to do this, just observing)
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