effective way to select last parameter of variadic template

Question

I know how to select first parameter of variadic template:

template< class...Args> struct select_first;
template< class A, class ...Args> struct          


        

Answer 1

With C++17, the cleanest way is

template
struct tag
{
    using type = T;
};

template
struct select_last
{
    // Use a fold-expression to fold the comma operator over the parameter pack.
    using type = typename decltype((tag{}, ...))::type;
};

with O(1) instantiation depth.