Transform variadic template parameters to another types

Question

How to transform types from variadic template parameters to another type?

For example:

template 
struct single
{
   std::tuple&l         


        

Answer 1

You can do more than just expand a variadic parameter pack as a plain list: you can expand an expression too. You can therefore have m_sequences be a tuple of vectors rather than a tuple of the elements:

template 
struct sequences
{
   std::tuple...> m_sequences;
};

You can also do nifty tricks with parameter packs to pick the appropriate element from the vector:

template struct indices_holder
{};

template >
struct make_indices_impl;

template
struct make_indices_impl >
{
    typedef typename make_indices_impl<
        index_to_add-1,
        indices_holder >::type type;
};

template
struct make_indices_impl<0,indices_holder >
{
    typedef indices_holder  type;
};

template
typename make_indices_impl::type make_indices()
{
    return typename make_indices_impl::type();
}



template 
struct sequences
{
    std::tuple...> m_sequences;

    template
    std::tuple get_impl(size_t pos,indices_holder)
    {
        return std::make_tuple(std::get(m_sequences)[pos]...);
    }

    std::tuple get(size_t pos)
    {
        return get_impl(pos,make_indices());
    }
};