Creating a sub-tuple starting from a std::tuple

Question

Let us suppose that a std::tuple is given. I would like to create a new std::tuple whose types are the ones indexed in [

Answer 1

Subrange from tuple with boundary checking, without declaring "helper classes":

template ())>
struct sub_range;

template 
struct sub_range, std::index_sequence>
{
    static_assert(elems <= sizeof...(args) - starting, "sub range is out of bounds!");
    using tuple = std::tuple> ...>;
};

Usage:

struct a0;
...
struct a8;

using range_outer = std::tuple;
sub_range<2, 3, range_outer>::tuple; //std::tuple