nealrichardson commented on code in PR #43351:
URL: https://github.com/apache/arrow/pull/43351#discussion_r1689716982
##########
r/src/arrow_cpp11.h:
##########
@@ -138,7 +138,12 @@ inline R_xlen_t r_string_size(SEXP s) {
} // namespace unsafe
inline SEXP utf8_strings(SEXP x) {
- return cpp11::unwind_protect([x] {
+ return cpp11::unwind_protect([&] {
+ // ensure that x is not actually altrep first
+ bool was_altrep = ALTREP(x);
+ if (was_altrep) {
+ x = PROTECT(Rf_duplicate(x));
Review Comment:
Add a comment about why we have to duplicate?
##########
r/src/arrow_cpp11.h:
##########
@@ -152,6 +157,9 @@ inline SEXP utf8_strings(SEXP x) {
SET_STRING_ELT(x, i, Rf_mkCharCE(Rf_translateCharUTF8(s), CE_UTF8));
Review Comment:
Did we want to check whether `Rf_translateCharUTF8()` actually modified
anything? Or do we trust that `SET_STRING_ELT` is a no-op in that case? I would
imagine that in most cases, we already have ascii/utf-8 strings, so this whole
function should be basically free. That should be easily verified by
microbenchmarking.
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