c++ - 压入和弹出 std::tuple 的第一个元素

Question

我正在用这种方式用可变数量的参数(和不同类型)在 C++ 中编写一个函数

template<typename ...Ts>
void myFunction(Ts ...args)
{
    //create std::tuple to access and manipulate single elements of the pack
    auto myTuple = std::make_tuple(args...);    

    //do stuff

    return;
}

我想做的，但我不知道怎么做，是从元组中压入和弹出元素，特别是第一个元素......类似

//remove the first element of the tuple thereby decreasing its size by one
myTuple.pop_front()

//add addThis as the first element of the tuple thereby increasing its size by one
myTuple.push_front(addThis)

这可能吗？

Answer 1

你可以做类似的事情

template <typename T, typename Tuple>
auto push_front(const T& t, const Tuple& tuple)
{
    return std::tuple_cat(std::make_tuple(t), tuple);
}

template <typename Tuple, std::size_t ... Is>
auto pop_front_impl(const Tuple& tuple, std::index_sequence<Is...>)
{
    return std::make_tuple(std::get<1 + Is>(tuple)...);
}

template <typename Tuple>
auto pop_front(const Tuple& tuple)
{
    return pop_front_impl(tuple,
                          std::make_index_sequence<std::tuple_size<Tuple>::value - 1>());
}

Demo

请注意，它非常基本，不处理引用元组或 const 限定类型的元组，但它可能就足够了。