Consider:
std::vector<double> u, v;
#pragma omp parallel for
for (std::size_t i = 0u; i < u.size(); ++i)
u[i] += v[i];
To express similar code with the C++17 parallel algorithms, the solution I found so far is to use the two input ranges version of std::transform:
std::transform(std::execution::par_unseq,
std::begin(u), std::end(u), std::begin(v), std::begin(u),
std::plus())
which I don't like at all because it bypasses the += operator of my types and in my real use case leads to much more verbose (4 times longer) code than the original OpenMP code (I cannot just use std::plus because I have to first make an operation on the RHS range elements).
Is there another algorithm that I oversight?
Note also that if I use ranges::zip the code won't run in parallel in GCC 9 because if iterator_category is not at least forward_iterator the PSTL back-end falls back to the sequential algorithm: https://godbolt.org/z/XGtPwc.
