[GitHub] [arrow] romainfrancois commented on a change in pull request #8256: ARROW-9001: [R] Box outputs as correct type in call_function

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romainfrancois commented on a change in pull request #8256:
URL: https://github.com/apache/arrow/pull/8256#discussion_r494775017



##########
File path: r/src/arrow_cpp11.h
##########
@@ -310,4 +312,32 @@ enable_if_enum<E, SEXP> as_sexp(E e) {
   return as_sexp(static_cast<int>(e));
 }
 
+template <typename T>
+SEXP R6_make(SEXP symbol, SEXP fun_symbol, const std::shared_ptr<T>& x) {
+  if (x == nullptr) {
+    return R_NilValue;
+  }
+  cpp11::external_pointer<std::shared_ptr<T>> xp(new std::shared_ptr<T>(x));
+
+  // make call:  <symbol>$new(<x>)
+  SEXP call = PROTECT(Rf_lang3(R_DollarSymbol, symbol, fun_symbol));
+  SEXP call2 = PROTECT(Rf_lang2(call, xp));
+
+  // and then eval:
+  SEXP r6 = PROTECT(Rf_eval(call2, arrow::r::ns::arrow));
+
+  UNPROTECT(3);
+  return r6;

Review comment:
       Perhaps this is more of a hypothetical `cpp11::call` thing, e.g. 
   
   ```cpp
   cpp11::call call(cpp11::call(R_DollarSymbol, symbol, fun_symbol), xp);
   cpp11::sexp result = call.eval(arrow::r::ns::arrow);
   ```
   
   Then I guess `cpp11::function` could factor out some of its logic in `cpp11::call` 
   




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