Function flatten

include/cute/algorithm/tuple_algorithms.hpp:564–579

//   and leave non-tuple untouched.
template <class T>
CUTE_HOST_DEVICE constexpr
auto
flatten(T const& t)
{
  if constexpr (is_tuple<T>::value) {
    if constexpr (is_flat<T>::value) {      // Shortcut for perf
      return t;
    } else {
      return filter_tuple(t, [](auto const& a) { return flatten_to_tuple(a); });
    }
  } else {
    return t;
  }

  CUTE_GCC_UNREACHABLE;
}

namespace detail {