I think the main problem is that it's easy to use your class incorrectly.
For example:
- What happens if your map is destructed? The SEXPs it is handling are
effectively leaked.
- What if you copy your map? Since SEXPs are pointers, you now have two
maps containing the same pointers, and if you were to attempt to remove a
SEXP from both maps problems would occur.
Rather than attempting to manage the lifetime of these R objects in your
map's methods, it's better to have wrapper classes that manage the lifetime
of a single SEXP -- ie, what Rcpp does with its classes.
You might consider just using e.g. std::unordered_map<T, Rcpp::RObject> if
you need to map some arbitrary types to R objects.
Best,
Kevin
On Thu, Aug 16, 2018 at 1:11 AM Simon Dirmeier <simon.dirme...@web.de>
wrote:
> Dear all,
> I have a question about *R_PreserveObject *and* R_ReleaseObject *and thought
> this would be good place to post it.
> I apologize if the question is not suitable or naive.
>
> Suppose I have something like the class below for which I use Rcpp-modules
> to extend it to R (code not shown).
> I use "insert" to add key-value pair to a map and "remove" to remove an
> entry.
>
> I am not having memory issues or so, but the solution seems wrong to me
> and I am concerned that it causes problems.
> Could you please give me some advice if this implementation is wrong or
> unefficient?
>
> Thank you in advance.
> Best,
> Simon
>
> template<typename T>
> class map
> {
> public:
> map() = default;
>
> size_t size()
> {
> return map_.size();
> }
>
> void insert(T& t, SEXP u)
> {
> SEXP s = Rf_duplicate(VECTOR_ELT(u, i));
> R_PreserveObject(s);
>
> map_.insert(std::pair<T, SEXP>(t[i], s));
> }
>
> void remove(T& t)
> {
> auto iter = map_.equal_range(t);
> for (auto it = iter.first; it != iter.second; ++it)
> {
> R_ReleaseObject(it->second);
> }
> map_.erase(t);
> }
>
> private:
> std::unordered_map<T, SEXP> map_;
> };
>
>
> _______________________________________________
> Rcpp-devel mailing list
> Rcpp-devel@lists.r-forge.r-project.org
> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
_______________________________________________
Rcpp-devel mailing list
Rcpp-devel@lists.r-forge.r-project.org
https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
