constexpr for loop

constexpr_for.cpp

#include <cassert>
#include <iostream>
#include <tuple>

namespace details
{

template <size_t v>
struct ConstexprNum
{
    static constexpr auto value = v;
    constexpr operator size_t() { return v; }
};

template <size_t i, size_t n, typename F>
void ConstexprForIter(F func)
{
    if constexpr (i < n)
    {
        func(ConstexprNum<i>{});
        ConstexprForIter<i + 1, n, F>(func);
    }
}

template <size_t i, size_t n, typename F>
void ConstexprForIter512(F func)
{
    if constexpr (i < n)
    {
        ConstexprForIter<i, std::min(i + 512, n), F>(func);
        ConstexprForIter512<i + 512, n, F>(func);
    }
}

}  // namespace details

template <size_t n, typename F>
void ConstexprFor(F func)
{
    details::ConstexprForIter512<0, n, F>(func);
}

int main()
{
    std::tuple t = std::make_tuple(0, 1, 2, 3, 4);
    constexpr auto t_size = std::tuple_size_v<decltype(t)>;

    ConstexprFor<t_size>([&](auto i)
    {
        std::cout << i << " " << std::get<i>(t) << std::endl;
    });

    constexpr size_t big_i = 2048;
    size_t cnt = 0;
    ConstexprFor<big_i>([&](auto i) { cnt += i; });
    assert(cnt == (big_i - 1) * big_i / 2);
}