[GitHub] [arrow] romainfrancois commented on a change in pull request #11919: ARROW-14804: [R] import_from_c() / export_to_c() methods should accept external pointers

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romainfrancois commented on a change in pull request #11919:
URL: https://github.com/apache/arrow/pull/11919#discussion_r766524355



##########
File path: r/src/py-to-r.cpp
##########
@@ -21,6 +21,38 @@
 
 #include <arrow/c/bridge.h>
 
+// [[arrow::export]]
+double external_pointer_addr_double(SEXP external_pointer) {
+  // potentially lossy conversion to double needed for the current
+  // implementation of import/export to Python
+  return reinterpret_cast<uintptr_t>(R_ExternalPtrAddr(external_pointer));

Review comment:
       Can this be something like ?
   
   ```c
   double out;
   void* ptr = R_ExternalPtrAddr(external_pointer);
   memcpy(&out, R_ExternalPtrAddr(external_pointer), sizeof(double));
   return out;
   ```

##########
File path: r/src/py-to-r.cpp
##########
@@ -21,6 +21,38 @@
 
 #include <arrow/c/bridge.h>
 
+// [[arrow::export]]
+double external_pointer_addr_double(SEXP external_pointer) {
+  // potentially lossy conversion to double needed for the current
+  // implementation of import/export to Python
+  return reinterpret_cast<uintptr_t>(R_ExternalPtrAddr(external_pointer));

Review comment:
       It seems to be what is done in `external_pointer_addr_integer64()` below. Maybe if this returned a `cpp11::doubles` ?




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