zerocost.cc

#include <type_traits>


template <typename T, typename = std::enable_if_t<std::is_compound_v<T>>>
constexpr T sum(const T& v) noexcept
{
    return v;
}


template <typename T, typename = std::enable_if_t<!std::is_compound_v<T>>>
constexpr T sum(T v) noexcept
{
    return v;
}


template <typename T, typename... Args, typename = std::enable_if_t<std::is_compound_v<T>>>
constexpr T sum(const T& first, Args... args) noexcept
{
    return sum(first, sum(args...));
}


template <typename T, typename... Args, typename = std::enable_if_t<!std::is_compound_v<T>>>
constexpr T sum(T first, Args... args) noexcept
{
    return sum(first, sum(args...));
}


struct tuple
{
    int first;
    int second;
};


constexpr tuple sum(const tuple& a, const tuple& b)
{
    return tuple{a.first + b.first, a.second + b.second};
}



int main()
{
    auto n = sum(tuple{1, 1}, tuple{2, 2}, tuple{3, 3});
    return n.first;
}