c++ - template parameter packs access Nth type and Nth element

Question

The following paper is the first proposal I found for template parameter packs.

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1603.pdf

At page 16, it talks about introducing two new operators [] and <> for accessing parameter pack elements and parameter pack types.

The suggested syntax for such an operator involves two new operators: .[] to access values and .<> to access types. For instance:

template<int N, typename Tuple> struct tuple_element;
template<int N, ... Elements>
struct tuple_element<tuple<Elements...> >
{
    typedef Elements.<N> type;
};

template<int N, ... Elements>
Elements.<N>& get(tuple<Elements...>& t)
{ return t.[N]; }

template<int N, ... Elements>
const Elements.<N>& get(const tuple<Elements...>& t)
{ return t.[N]; }

So where are these operators? If there is none, what is their replacement?

Answer 1

Others have already answered that it can be done via std::tuple. If you want to access the Nth type of a parameter pack, you may find the following metafunction handy:

template<int N, typename... Ts> using NthTypeOf =
        typename std::tuple_element<N, std::tuple<Ts...>>::type;

Usage:

using ThirdType = NthTypeOf<2, Ts...>;