Multiple Outputs/zip_iterator as output

[rgreenblatt]

Is there any way to have multiple outputs in general? zip_iterators work for multiple inputs, but don't allow for multiple outputs. I would ideally expect the following to work, but it doesn't:

#include <boost/compute.hpp>
#include <iostream>
#include <vector>

namespace bc = boost::compute;

int main(int argc, char *argv[]) {
  bc::vector<int> data(bc::counting_iterator<int>(0),
                       bc::counting_iterator<int>(10));
  bc::vector<int> output_1(data.size());
  bc::vector<int> output_2(data.size());

  // BOOST_COMPUTE_FUNCTION can't handle templated return types
  auto duplicate = bc::detail::make_function_impl<boost::tuple<int, int>(int)>(
      "duplicate", BOOST_COMPUTE_STRINGIZE_SOURCE((int value)),
      BOOST_COMPUTE_STRINGIZE_SOURCE({
        return (boost_tuple_int_int_t){value, value};
      }));

  bc::transform(data.begin(), data.end(),
                bc::make_zip_iterator(
                    boost::make_tuple(output_1.begin(), output_2.begin())),
                duplicate);

  std::vector<int> output_1_cpu(data.size());
  std::vector<int> output_2_cpu(data.size());
  bc::copy(output_1.begin(), output_1.end(), output_1_cpu.begin());
  bc::copy(output_2.begin(), output_2.end(), output_2_cpu.begin());
  for (size_t i = 0; i < output_1_cpu.size(); ++i) {
    std::cout << "1: " << output_1_cpu[i] << " 2: " << output_2_cpu[i] << "\n";
  }

  return 0;
}

It fails because the generated kernel doesn't assign to output_1 and output_2. Instead, a new struct/tuple is constructed and assigned to.