#include <tuple>
#include <cassert>

int main()
{
    std::tuple<int>    t1 { 1 };
    std::tuple<double> t2 { 2.3 };
    auto               t3 { merge(t1, t2) };
    std::tuple<int>    t4 { 4 };
    std::tuple<int>    t5 { 5 };
    auto               t6 { merge(t4, t5) };
    auto               t7 { merge(t3, t6) };
    
    assert( (t3 == std::make_tuple(1, 2.3)) );
    assert( (t6 == std::make_tuple(4, 5)) );
    assert( (t7 == std::make_tuple(1, 2.3, 4, 5)) );
}