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

struct Tracked {
    enum class State { CONSTRUCTED, MOVED_FROM, DESTROYED };
    State state;

    Tracked() : state{State::CONSTRUCTED} { std::cout << "Constructing " << (void*) this << std::endl; }

    Tracked(Tracked const& t) : state{State::CONSTRUCTED} {
        std::cout << "Copy-constructing " <<  (void*) this << " from " << (void *) &t << std::endl; 
        assert(t.state != State::MOVED_FROM && "copying a moved-from object");
        assert(t.state != State::DESTROYED  && "copying a destroyed object");
    }

    Tracked(Tracked&& t) : state{State::CONSTRUCTED} {
        std::cout << "Move-constructing " <<  (void*) this << " from " << (void *) &t << std::endl; 
        assert(t.state != State::MOVED_FROM && "double moving from an object");
        assert(t.state != State::DESTROYED  && "moving from a destroyed object");
        t.state = State::MOVED_FROM;
    }

    ~Tracked() {
        std::cout << "Destroying " << (void*) this << std::endl; 
        assert(state != State::DESTROYED && "double-destroying an object");
        state = State::DESTROYED;
    }
};

int main() {
    Tracked v;
    auto t1 = std::make_tuple(v);
//  auto t1 = std::make_tuple(Tracked{});
    {
        auto t2 = std::make_tuple(t1);
//      auto t2 = std::make_tuple(std::move(t1));
        {
            std::cout << "  Creating t3" << std::endl;
//          auto t3 = std::tuple_cat(t2);
            auto t3 = std::tuple_cat(std::move(t2)); // move
            std::cout << "  Destroying t3" << std::endl;
        }
    }
}

int main() {
    auto empty = std::make_tuple();
    auto singleton = std::make_tuple(Tracked{});
    std::tuple_cat(empty, std::make_tuple(singleton));
}