Is it possible to go from `std::array` to `parameter pack` or `variadic`?

yes

you just need to build an index sequence
it's the same as working with a tuple, basically
although tbh it's a bit rare to go from array to parameter pack
because all the types are the same. So you're going from something that's easy to work with but more constrained, to something less constrained and harder to work with.

template <typename T, std::size_t N, std::size ... Is>

T buildT_helper(std::index_sequence<Is...>) {

    std::array<complexclass, N> array;

    ...

    return {array[Is]...};

}



template <typename T, std::size_t N>

T buildT() { return buildT_helper(std::make_index_sequence<N>{}); }

 
 
Seems like maybe it would be simpler to just give `T` a constructor taking an array?

if you control T
but, I don't have broader context obviously... so if you want to stick with how you're doing it, the code above should help