I have some trouble using C++17 parallel execution algorithm with Boost iterators on MSVC. Here is my code:
#include <vector>
#include <execution>
#include <boost/range/combine.hpp>
int main(void)
{
std::vector<double> const v1(20, 1);
std::vector<double> const v2(20, 2);
std::vector<double> v_out;
v_out.resize(20);
auto const & combi = boost::combine(v1, v2);
auto const run = [](auto const & v)
{
return boost::get<0>(v) + boost::get<1>(v);
};
std::transform(std::execution::par, combi.begin(), combi.end(), v_out.begin(), run);
return 0;
}
I get the following error:
error C2338: Parallel algorithms require forward iterators or stronger.
This seems due to the Boost zip iterator but I don't understand why since it compiles without error on GCC. What am I missing here ? Is this a bug implementation in Visual C++ ?
zip iterators can only be input in the C++17 iterator hierarchy because their reference types are not real references.
It is undefined behavior to passing an input iterator to a parallel algorithm. MSVC's implementation happens to check the precondition more aggressively than GCC's.