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

If you are willing to strip references blindly from your type list (which is quite often the case: either you know they are references, or you don't care), you can do this with little machinery outside of std. Basically stuff the data into a tuple or tie, then use std::get( tuple or tie ) to extract the last element.

You can do this in a pure-type context using std::declval< std::tuple >() and decltype, and possibly std::remove_reference.

As an example, suppose you have a variardic set of arguments, and you want to return the last argument ignoring the rest:

#define RETURNS(x) ->decltype(x) { return (x); }

template
auto get_last( Args&&... args )
  RETURNS( std::get< sizeof...(Args)-1 >( std::tie(std::forward(args)...) ) )

we can then use this in another function:

template
void foo( Args&&... args ) {
  auto&& last = get_last(std::forward(args)...);
}