Appendix B - tupleAccumulate

Implementation of tupleAccumulate() function. Namespace details contains some helper classes.

namespace details
{

template <std::size_t TRem>
class TupleAccumulateHelper
{
public:
    template <typename TTuple, typename TValue, typename TFunc>
    static constexpr TValue exec(TTuple&& tuple, const TValue& value, TFunc&& func)
    {
        using Tuple = typename std::decay<TTuple>::type;
        static_assert(TRem <= std::tuple_size<Tuple>::value, "Incorrect TRem");

        return TupleAccumulateHelper<TRem - 1>::exec(
                    std::forward<TTuple>(tuple),
                    func(value, std::get<std::tuple_size<Tuple>::value - TRem>(std::forward<TTuple>(tuple))),
                    std::forward<TFunc>(func));
    }
};

template <>
class TupleAccumulateHelper<0>
{

public:
    template <typename TTuple, typename TValue, typename TFunc>
    static constexpr TValue exec(TTuple&& tuple, const TValue& value, TFunc&& func)
    {
        return value;
    }
};

}  // namespace details

template <typename TTuple, typename TValue, typename TFunc>
constexpr TValue tupleAccumulate(TTuple&& tuple, const TValue& value, TFunc&& func)
{
    using Tuple = typename std::decay<TTuple>::type;

    return details::TupleAccumulateHelper<std::tuple_size<Tuple>::value>::exec(
                std::forward<TTuple>(tuple),
                value,
                std::forward<TFunc>(func));
}