Class vectorize_helper

include/pybind11/numpy.h:2127–2273

template <typename Func, typename Return, typename... Args>
struct vectorize_helper {

// NVCC for some reason breaks if NVectorized is private
#ifdef __CUDACC__
public:
#else
private:
#endif

    static constexpr size_t N = sizeof...(Args);
    static constexpr size_t NVectorized = constexpr_sum(vectorize_arg<Args>::vectorize...);
    static_assert(
        NVectorized >= 1,
        "pybind11::vectorize(...) requires a function with at least one vectorizable argument");

public:
    template <typename T,
              // SFINAE to prevent shadowing the copy constructor.
              typename = detail::enable_if_t<
                  !std::is_same<vectorize_helper, typename std::decay<T>::type>::value>>
    explicit vectorize_helper(T &&f) : f(std::forward<T>(f)) {}

    object operator()(typename vectorize_arg<Args>::type... args) {
        return run(args...,
                   make_index_sequence<N>(),
                   select_indices<vectorize_arg<Args>::vectorize...>(),
                   make_index_sequence<NVectorized>());
    }

private:
    remove_reference_t<Func> f;

    // Internal compiler error in MSVC 19.16.27025.1 (Visual Studio 2017 15.9.4), when compiling
    // with "/permissive-" flag when arg_call_types is manually inlined.
    using arg_call_types = std::tuple<typename vectorize_arg<Args>::call_type...>;
    template <size_t Index>
    using param_n_t = typename std::tuple_element<Index, arg_call_types>::type;

    using returned_array = vectorize_returned_array<Func, Return, Args...>;

    // Runs a vectorized function given arguments tuple and three index sequences:
    //     - Index is the full set of 0 ... (N-1) argument indices;
    //     - VIndex is the subset of argument indices with vectorized parameters, letting us access
    //       vectorized arguments (anything not in this sequence is passed through)
    //     - BIndex is a incremental sequence (beginning at 0) of the same size as VIndex, so that
    //       we can store vectorized buffer_infos in an array (argument VIndex has its buffer at
    //       index BIndex in the array).
    template <size_t... Index, size_t... VIndex, size_t... BIndex>
    object run(typename vectorize_arg<Args>::type &...args,
               index_sequence<Index...> i_seq,
               index_sequence<VIndex...> vi_seq,
               index_sequence<BIndex...> bi_seq) {

        // Pointers to values the function was called with; the vectorized ones set here will start
        // out as array_t<T> pointers, but they will be changed them to T pointers before we make
        // call the wrapped function.  Non-vectorized pointers are left as-is.
        std::array<void *, N> params{{reinterpret_cast<void *>(&args)...}};