Over in the cmdstanr package we recently added support for passing std::tuple<> types between c++ and R by treating it as a List, and I was hoping to put together a PR to add it to Rcpp directly (I checked the issues and PRs but I couldn't find anything).
Should these overloads/specifications live in ListOf or VectorBase (or somewhere else completely)?
Also feel completely free to let me know if I'm handling the conversions in a way that's fundamentally wrong/inefficient!
The implementation is below, and just a note that the stan::math::apply is just c++11 implementation of std::apply:
#include <stan/math/prim/functor/apply.hpp>
#include <Rcpp.h>
namespace Rcpp {
namespace traits {
template <typename... T>
class Exporter<std::tuple<T...>> {
private:
Rcpp::List list_x;
template<std::size_t... I>
auto get_impl(std::index_sequence<I...> i) {
return std::make_tuple(Rcpp::as<T>(list_x[I].get())...);
}
public:
Exporter(SEXP x) : list_x(x) { }
std::tuple<T...> get() {
return get_impl(std::index_sequence_for<T...>{});
}
};
}
template <typename... T>
SEXP wrap(const std::tuple<T...>& x) {
return stan::math::apply([](const auto&... args) {
return Rcpp::List::create(Rcpp::wrap(args)...);
}, x);
}
}
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