jeudi 6 mai 2021

Arithmetic on all but the last components of tuples in C++

Getting inspiration from this question, I managed to implement a function which takes two tuples as input and return a tuple which components are the min of each components of the tuples given in input.

template<typename T, T...>
struct integer_sequence { };

template<std::size_t N, std::size_t... I>
struct gen_indices : gen_indices<(N - 1), (N - 1), I...> { };
template<std::size_t... I>
struct gen_indices<0, I...> : integer_sequence<std::size_t, I...> { };

template <typename ... T, std::size_t ... I>
std::tuple<T...> min_tuple_impl(
        const std::tuple<T...>& t1,
        const std::tuple<T...>& t2,
        integer_sequence<std::size_t, I...>)
{
    return { (std::min(std::get<I>(t1), std::get<I>(t2)))... };
}

template <typename ... T>
std::tuple<T...> min_tuple(
        const std::tuple<T...>& t1,
        const std::tuple<T...>& t2)
{
    return min_tuple_impl(t1, t2, gen_indices<sizeof...(T)>{});
}

Now, I would like it to work on all components but the last one.

std::tuple<int, int, int> t1 {10, 20, 30}
std::tuple<int, int, int> t2 {15, 15, 15}
min_tuple(t1, t2) // == {10, 15, 30}, for the last one, always keep the component of t1

How could I get this in C++11?

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