Clarify

Author: krlmlr

inst/include/cpp11/external_pointer.hpp

@@ -72,7 +72,9 @@ class external_pointer {
   }
 
   external_pointer& operator=(external_pointer&& rhs) noexcept {
+    // This works even if `this == &rhs` because `data_` (a `cpp11::sexp`) handles the underlying resource.
     data_ = rhs.data_;
+    // Order matters: first assign, then clear the RHS.
     rhs.data_ = R_NilValue;
     return *this;
   }